umu.sePublications
Change search
Refine search result
1234 51 - 100 of 186
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 51. Hou, Song
    et al.
    Dlugogorski, Bogdan Z.
    Mackie, John C.
    Kennedy, Eric M.
    Jansson, Stina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Altarawneh, Mohammednoor
    Oxidation of 4-bromo-4'-chlorobiphenyl, model species for forming mixed halogenated aromatic compounds2017In: International Journal of Environment and Pollution, ISSN 0957-4352, E-ISSN 1741-5101, Vol. 61, no 3-4, p. 243-260Article in journal (Refereed)
    Abstract [en]

    This contribution reports results from the gas-phase oxidation of 4-bromo-4'-chlorobiphenyl (4,4'-BCB) in order to fathom the formation of toxic species produced during the combustion of mixed halogenated aromatics. In their own right, mixed polybrominated/polychlorinated biphenyls (PXBs) represent a new class of environmental contaminants, recently detected in food and human tissues. Gas chromatography-quadrupole mass spectrometry (GC-QMS), gas chromatography-quadrupole time of flight mass spectrometry (GC-QTOFMS), Fourier transform infrared spectroscopy (FTIR) and ion chromatography (IC) served to analyse the volatile and semi-volatile organic compounds (V/SVOCs), including mixed halogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs), and gaseous products including HBr/HCl. The selection of non-ortho substituted PXB as a model species yields a large number of halogenated compounds, including monochloro- and monobromobenzene and higher halogenated benzenes and naphthalenes and derivatives of halogenated benzenes (such as 1-chloro-4-ethynylbenzene). We also detect small amounts of chlorinated and mixed halogenated dibenzofurans. The present study provides insights into the formation of several classes of halogenated and mixed-halogenated pollutants in combustion processes involving both bromine and chlorine sources, such as those of brominated flame retardants and PVC plastics.

  • 52. Hutinel, Marion
    et al.
    Huijbers, Patricia Maria Catharina
    Fick, Jerker
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ahrenk, Christina
    Larsson, Dan Goran Joakim
    Flach, Carl-Fredrik
    Population-level surveillance of antibiotic resistance in Escherichia coli through sewage analysis2019In: Eurosurveillance, ISSN 1025-496X, E-ISSN 1560-7917, Vol. 24, no 37, p. 6-16, article id 1800497Article in journal (Refereed)
    Abstract [en]

    Introduction: The occurrence of antibiotic resistance in faecal bacteria in sewage is likely to reflect the current local clinical resistance situation.

    Aim: This observational study investigated the relationship between Escherichia coli resistance rates in sewage and clinical samples representing the same human populations.

    Methods: E. coli were isolated from eight hospital (n=721 isolates) and six municipal (n=531 isolates) sewage samples, over 1year in Gothenburg, Sweden. An inexpensive broth screening method was validated against disk diffusion and applied to determine resistance against 11 antibiotics in sewage isolates. Resistance data on E. coli isolated from clinical samples from corresponding local hospital and primary care patients were collected during the same year and compared with those of the sewage isolates by linear regression.

    Results: E. coli resistance rates derived from hospital sewage and hospital patients strongly correlated (r(2) = 0.95 for urine and 0.89 for blood samples), as did resistance rates in E. coli from municipal sewage and primary care urine samples (r(2)=0.82). Resistance rates in hospital sewage isolates were close to those in hospital clinical isolates while resistance rates in municipal sewage isolates were about half of those measured in primary care isolates. Resistance rates in municipal sewage isolates were more stable between sampling occasions than those from hospital sewage.

    Conclusion: Our findings provide support for development of a low-cost, sewage-based surveillance system for antibiotic resistance in E. coli, which could complement current monitoring systems and provide clinically relevant antibiotic resistance data for countries and regions where surveillance is lacking.

  • 53.
    Israelsson, Marlen
    et al.
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Clinical chemistry.
    Brattsand, Ralph
    Brattsand, Göran
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Clinical chemistry.
    20α- and 20β-dihydrocortisone may interfere in LC-MS/MS determination of cortisol in saliva and urine2018In: Annals of Clinical Biochemistry, ISSN 0004-5632, E-ISSN 1758-1001, Vol. 55, no 3, p. 341-347Article in journal (Refereed)
    Abstract [en]

    Background: LC-MS/MS methods offer high selectivity in cortisol determinations. However, endogenous steroid metabolites may still interfere and compromise the results, for example in the diagnosis of Cushing's syndrome. Erroneously elevated cortisol may, in particular, be misleading at the low concentrations found in salivary samples obtained at late night and after dexamethasone suppression.

    Methods: Interferences in our LC-MS/MS method used for determination of cortisol in saliva and urine were identified by comparing their retention times and mass spectra with those of pure candidate substances. The chromatographic conditions used in our LC-MS/MS method, including column and mobile phase gradient, were varied in order to separate the target compound from the interferences.

    Results: Two interferences, which were co-eluting or eluting close to cortisol in our original method, were successfully separated from cortisol by adjustment of the chromatographic conditions. These interferences were found in both urine and saliva and were identified as the two endogenous cortisol isomers 20- and 20-dihydrocortisone. The isomers share molecular mass and mass spectrometric fragmentation pattern with cortisol using electrospray ionization in the positive-ion mode. Both give rise to the transitions m/z 363.1>121.1, 363.1>115.1 and 363.1>97.1. In our original LC-MS/MS setup, the 20-dihydrocortisone co-eluted with cortisol in the chromatography step resulting in false high determinations.

    Conclusions: Cortisol determination by LC-MS/MS may suffer from erroneously elevated results unless 20- and 20-dihydrocortisone are chromatographically separated from cortisol.

  • 54. Jiang, Ruyuan
    et al.
    Liu, Niantao
    Gao, Sanshuang
    Mamat, Xamxikamar
    Su, Yuhong
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Li, Yongtao
    Hu, Xun
    Hu, Guangzhi
    A Facile Electrochemical Sensor Based on PyTS-CNTs for Simultaneous Determination of Cadmium and Lead Ions2018In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 18, no 5, article id 1567Article in journal (Refereed)
    Abstract [en]

    A simple and easy method was implemented for the contemporary detection of cadmium (Cd2+) and lead (Pb2+) ions using 1,3,6,8-pyrenetetrasulfonic acid sodium salt-functionalized carbon nanotubes nanocomposites (PyTS-CNTs). The morphology and composition of the obtained PyTS-CNTs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The experimental results confirmed that the fabricated PyTS-CNTs exhibited good selectivity and sensitivity for metal ion-sensing owing to the insertion of sulfonic acid groups. For Cd2+ and Pb2+, some of the electrochemical sensing parameters were evaluated by varying data such as the PyTS-CNT quantity loaded on the pyrolytic graphite electrode (PGE), pH of the acetate buffer, deposition time, and deposition potential. These parameters were optimized with differential pulse anodic sweeping voltammetry (DPASV). Under the optimal condition, the stripping peak current of the PyTS-CNTs/Nafion/PGE varies linearly with the heavy metal ion concentration, ranging from 1.0 mu g L-1 to 90 mu g L-1 for Cd2+ and from 1.0 mu g L-1 to 110 mu g L-1 for Pb2+. The limits of detection were estimated to be approximately 0.8 mu g L-1 for Cd2+ and 0.02 mu g L-1 for Pb2+. The proposed PyTS CNTs/Nafion/PGE can be used as a rapid, simple, and controllable electrochemical sensor for the determination of toxic Cd2+ and Pb2+.

  • 55.
    Jiang, Wen
    Umeå University, Faculty of Science and Technology, Chemistry.
    Zwitterionic Separation Materials for Liquid Chromatography and Capillary Electrophoresis: Synthesis, Characterization and Application for Inorganic Ion and Biomolecule Separations2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Liquid Chromatography (LC) and Capillary Electrophoresis (CE) are modern analytical techniques that play very important roles in many areas of modern science such as life science, biotechnology, biomedicine, environmental studies, and development of pharmaceutics. Even though these two techniques have existed and been subjected to studies for several decades, the developments of new separation materials for them are still very important till now in order to meet the different new demands for improvement from other disciplines in science.

    In this doctoral thesis, several novel covalently bonded sulfobetaine type zwitterionic separation materials are synthesized for the application in LC and CE. These materials carry both positively charged quaternary ammonium groups and negatively charged sulfonic groups, which result in a very low net surface charge compared to conventional separation materials with only anionic or cationic functional groups. Consequently, it is possible to employ these materials for separation of different ionic species under mild conditions. The surface properties have also been characterized, mainly by elemental analysis, sorption isotherm, ζ-potential measurements, and spectroscopic methods.

    By using packed zwitterionic columns for liquid chromatography, small inorganic anions or cations, and acidic or basic proteins can be independently and simultaneously separated in a single run using optimal sets of separation conditions. This is a unique property compared to conventional ionic separation material for LC. When fused silica capillaries coated with zwitterionic polymer are used for capillary electrophoresis, good separations can be achieved for solutes as different as inorganic anions, peptides, proteins, and tryptically digested proteins.

  • 56. Jogunola, Olatunde
    et al.
    Salmi, Tapio
    Leveneur, Sébastien
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Åbo Akademi, Johan Gadolin Process Chemistry Centre, Laboratory of Industrial Chemistry and Reaction Engineering, Åbo/Turku, Finland.
    Complexation equilibria studies of alkyl formate hydrolysis in the presence of 1-butylimidazole2017In: Thermochimica Acta, ISSN 0040-6031, E-ISSN 1872-762X, Vol. 652, p. 62-68Article in journal (Refereed)
    Abstract [en]

    Formic acid production by ethyl or methyl formate hydrolysis was improved using 1-butylimidazole as a complexing agent. The chemical process involved both hydrolysis and complexation steps. The complexation equilibria were investigated by deriving theoretical equations using the equilibrium constant of the hydrolysis step, the apparent formation constant of the complexation process and the initial concentration of the complexing agent. The treatment of the experimental results within the experimental domain indicated that an equimolar amount of the acid and the base did not lead to the complex formation. Experimental observation suggested that the derived equation could be simplified by assuming that the stoichiometric coefficient of the complexing agent was 0.5. The apparent reaction enthalpy obtained from this equation was compared to the experimental one using a Tian-Calvet calorimeter and a good agreement was found between them. FTIR spectroscopy was used to confirm the existence of the complex between formic acid and 1-butylimidazole.

  • 57.
    Johansson, Anders
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Infectious Diseases. Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Clinical Bacteriology.
    Petersen, Jeannine M
    Genotyping of Francisella tularensis, the causative agent of tularemia2010In: Journal of AOAC International, ISSN 1060-3271, E-ISSN 1944-7922, Vol. 93, no 6, p. 1930-1943Article in journal (Refereed)
    Abstract [en]

    Francisella tularensis is a facultative, intracellular, zoonotic pathogen and the causative agent of tularemia. Historically, F. tularensis has been subdivided into subspecies on the basis of phenotypic traits, including biochemical reactivity and virulence. More recently, a number of genotypic methods, ranging from relatively insensitive methods to full genome sequencing, have been used to investigate genetic diversity within F. tularensis. These analyses indicate that F. tularensis is a pathogen of low sequence diversity with pair-wise average nucleotide identities > 99.2% across subspecies. Nonetheless, genomic rearrangements and sequence deletions exist between and within F. tularensis subspecies, creating polymorphisms detectable by genotyping methods. Genetic subpopulations intermediate to the subspecies and strain level have been identified within F. tularensis subsp. tularensis and F. tularensis subsp. holarctica by several different typing methods. These genetic subpopulations have been associated with differences in disease severity, geographic distribution, and transmission patterns. For example, one F. tularensis subsp. tularensis subpopulation has been found to be significantly associated with mortality in humans. Additionally, genotypic analyses of Francisella spp. have provided information for use in the rational design of strain panels for validation of F. tularensis diagnostic tests. This review provides a guide to the various F. tularensis genotyping methods.

  • 58.
    Jonsson, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Emteborg, Malin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Heterocyclic compounds as catalysts in the peroxyoxalate chemiluminescence reaction of bis(2,4,6-trichlorophenyl)oxalate1998In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 361, no 3, p. 205-215Article in journal (Refereed)
    Abstract [en]

    Substituted imidazoles and leaving groups known from other areas of chemistry have been tested for catalytic efficiency in the peroxyoxalate chemiluminescence (PO-CL) reaction, using bis(2,4,6-trichlorophenyl)oxalate (TCPO) as reagent. Catalytic activity was found for 1,2,4-triazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole and 4,5-dichloroimidazole, while 2-mercaptoimidazole, 2-nitroimidazole, 4-nitroimidazole, benzimidazole, benzotriazole, thiazole, o-benzoic sulfimide, phthalimide, succinimide, 2(1H)-pyridone and 1,2,3-benzotriazine-4(3H)-one yielded no detectable chemiluminescence under the conditions used. None of the tested compounds was more efficient than imidazole in catalyzing the PO-CL reaction. Spectrophotometric measurements of the catalytic breakdown of TCPO showed that an intermediate was formed with almost all catalysts, and that intermediates that were more stable or present at lower concentration led to a reduced catalytic efficiency in the PO-CL reaction of TCPO.

  • 59.
    Jonsson, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Very fast peroxyoxalate chemiluminescence1999In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 400, no 1-3, p. 257-264Article in journal (Refereed)
    Abstract [en]

    Peroxyoxalate chemiluminescence (PO-CL) detection offers an advantage in chromatographic detection, by the virtue of its multiple unique selectivities and high sensitivity. However, many of the analytical separation techniques available today require observation times in the millisecond range to preserve the band resolution, and as the reaction kinetics of the PO-CL reaction is considerably slower, extra flow elements are needed to observe the reaction in a time window at maximum emission intensity. Since these flow elements increase the complexity of the system and contribute to band-broadening, the rational way to adapt PO-CL detection to miniaturised separation systems is to speed up the reaction, so that it emits an initial burst of light within the acceptable detection time-frame. Although this may result in a lower overall quantum yield, the actual detection sensitivity could be equal to, or better than slower PO-CL systems. By making careful selections of oxalic reagent and catalyst(s) the reaction can be fine-tuned to maximise the intensity. In this work, the time-dependent light emission from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) was studied under the catalytic influence of imidazole, 1,2,4-triazole, 4-dimethylaminopyridine (DMAP), and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) in acetonitrile. Both DMAP and DBU accelerated the reaction substantially, but the best combination of reaction speed and intensity was found for a mixture of 0.5 mM DBU and 5 mM 1,2,4-triazole, which reached its maximum emission after only 40 ms and had an emission intensity comparable to that seen with 5 mM imidazole as catalyst.

  • 60.
    Karimpour, Masoumeh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Multi-platform metabolomics assays to study the responsiveness of the human plasma and lung lavage metabolome2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Metabolomics as a field has been used to track changes and perturbations in the human body by investigating metabolite profiles indicating the change of metabolite levels over time and in response to different challenges. In this thesis work, the main focus was on applying multiplatform-metabolomics to study the human metabolome following exposure to perturbations, such as diet (in the form of a challenge meal) and exhaust emissions (air pollution exposure in a controlled setting). The cutting-edge analytical platforms used for this purpose were nuclear magnetic resonance (NMR), as well as gas chromatography (GC) and liquid chromatography (LC) coupled to mass spectrometry (MS). Each platform offered unique characterization features, allowing detection and identification of a specific range of metabolites. The use of multiplatform-metabolomics was found to enhance the metabolome coverage and to provide complementary findings that enabled a better understanding of the biochemical processes reflected by the metabolite profiles. Using non-targeted analysis, a wide range of unknown metabolites in plasma were identified during the postprandial stage after a well-defined challenge meal (in Paper I). In addition, a considerable number of metabolites were detected and identified in lung lavage fluid after biodiesel exhaust exposure compared to filtered air exposure (in Paper II). In parallel, using targeted analysis, both lung lavage and plasma fatty acid metabolites were detected and quantified in response to filtered air and biodiesel exhaust exposure (in Paper III and IV).

    Data processing of raw data followed by data analysis, using both univariate and multivariate methods, enabled changes occurring in metabolites levels to be screened and investigated. For the initial pilot postprandial study, the aim was to investigate the plasma metabolome response after a well-defined meal during the postprandial stage for two types of diet. It was found that independent of the background diet type, levels of metabolites returned to their baseline levels after three hours. This finding was taken into consideration for the biodiesel exhaust exposures studies, designed to limit the impact of dietary effects. Both targeted and non-targeted approaches resulted in important findings. For instance, different metabolite profiles were detected in bronchial wash (BW) compared to bronchoalveolar lavage (BAL) fluid with mainly NMR and LC-MS. Furthermore, biodiesel exhaust exposure resulted in different metabolite profiles as observed by GC-MS, especially in BAL. In addition, fatty acid metabolites in BW, BAL, and plasma were shown to be responsive to biodiesel exhaust exposure, as measured by a targeted LC-MS/MS protocol. In summary, the new analytical methods developed to investigate the responsiveness of the human plasma and lung lavage metabolome proved to be useful in an analytical perspective, and provided important biological findings. However, further studies are needed to validate these results.

  • 61.
    Karimpour, Masoumeh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Surowiec, Izabella
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wu, Junfang
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gouveia-Figueira, Sandra
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Pharmacology.
    Pinto, Rui
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Bioinformatics Infrastructure for Life Sciences, Sweden.
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Zivkovic, Angela M.
    Nording, Malin L.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Postprandial metabolomics: A pilot mass spectrometry and NMR study of the human plasma metabolome in response to a challenge meal2016In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 908, p. 121-131Article in journal (Refereed)
    Abstract [en]

    The study of postprandial metabolism is relevant for understanding metabolic diseases and characterizing personal responses to diet. We combined three analytical platforms – gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) – to validate a multi-platform approach for characterizing individual variation in the postprandial state. We analyzed the postprandial plasma metabolome by introducing, at three occasions, meal challenges on a usual diet, and 1.5 years later, on a modified background diet. The postprandial response was stable over time and largely independent of the background diet as revealed by all three analytical platforms. Coverage of the metabolome between NMR and GC-MS included more polar metabolites detectable only by NMR and more hydrophobic compounds detected by GC-MS. The variability across three separate testing occasions among the identified metabolites was in the range of 1.1–86% for GC-MS and 0.9–42% for NMR in the fasting state at baseline. For the LC-MS analysis, the coefficients of variation of the detected compounds in the fasting state at baseline were in the range of 2–97% for the positive and 4–69% for the negative mode. Multivariate analysis (MVA) of metabolites detected with GC-MS revealed that for both background diets, levels of postprandial amino acids and sugars increased whereas those of fatty acids decreased at 0.5 h after the meal was consumed, reflecting the expected response to the challenge meal. MVA of NMR data revealed increasing postprandial levels of amino acids and other organic acids together with decreasing levels of acetoacetate and 3-hydroxybutanoic acid, also independent of the background diet. Together these data show that the postprandial response to the same challenge meal was stable even though it was tested 1.5 years apart, and that it was largely independent of background diet. This work demonstrates the efficacy of a multi-platform metabolomics approach followed by multivariate and univariate data analysis for a broad-scale screen of the individual metabolome, particularly for studies using repeated measures to determine dietary response phenotype.

  • 62.
    Khan, Ghazanfar Ali
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Monitoring anti-infectives and antibiotic resistance genes: with focus on analytical method development, effects of antibiotics and national perspectives2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Antibiotics are biologically active and are globally used in humans and animal medicine for treatment and in sub-therapeutic amounts as growth promoters in animal husbandry, aquaculture and agriculture. After excretion, inappropriate disposal and discharge from drug production facilities they enter into water bodies either as intact drugs, metabolites or transformed products. In water environments they promote development of antibiotic resistance genes (ARGs) which could serve as a reservoir and be horizontally transferred to human-associated bacteria and thus contribute to AR proliferation. Measurement of antibiotics has been revolutionized with the usage of solid phase extraction (SPE) for enrichment followed by Liquid chromatography mass spectrometry (LC-MS). On-line SPE coupled to LC-MS/MS has the advantages of high sample throughput, low sample preparation time and minimal solvent utilization.  Constructed wetlands (CWs) are potential alternatives to conventional treatment plants to remove organic pollutants. A study at Plönninge, Halmstad was performed to assess the impact of bacterial community pattern and development of resistance in spiked (n=4) and control (n=4). CWs were spiked with antibiotics at environmentally relevant concentrations continuously for 25 days. Shannon Index (H’) were used to determine the bacterial diversity and real-time PCR detected and quantified antibiotic resistance genes (ARGs) sulI, tetA, tetB, erm, dfrA1, qnrS and vanB and class 1 integrons intI1. No significant differences in bacterial compositions or in ARGs or integron concentrations could be discerned between exposed and control wetlands. A study conducted in Northern Pakistan showed that the antibiotic levels in most studied rivers were comparable to surface water measurements in unpolluted sites in Europe and the US. However, high levels of antibiotics were detected in the river in close vicinity of the 10 million city Lahore, e.g. 4600 ng L−1 sulfamethoxazole. Highest detected levels were at one of the drug formulation facilities, with measured levels up to 49000 ng L−1 of sulfamethoxazole for example. The highest levels of ARGs detected, sul1 and dfrA1, were directly associated with the antibiotics detected at the highest concentrations, sulfamethoxazole and trimethoprim. In the study in UK, sewage epidemiology surveillance is used to measure the oseltamivir carboxylate (OC), metabolite of oseltamivir (parent drug) in twenty four time proportional hourly influent samples from two WWTPs and then back-calculations were made to assess the compliance of drug.  Predicted users of oseltamivir, based on measured OC in waste water, ranged from 3-4 and 120-154 people for the two WWTP catchments, respectively, which are consistent with the projected use from national antiviral allocation statistics, 3-8 and 108-270, respectively. Scenario analysis suggests compliance was likely between 45-60% in the study regions. 

  • 63.
    Khokarale, Santosh G.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry & Reaction Engineering, Department of Chemical Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, FI-20500 Åbo - Turku, Finland.
    Metal free synthesis of ethylene and propylene carbonate from alkylene halohydrin and CO2 at room temperature2019In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 58, p. 34023-34031Article in journal (Refereed)
    Abstract [en]

    Herein we describe a metal free and one-pot pathway for the synthesis of industrially important cyclic carbonates such as ethylene carbonate (EC) and propylene carbonates (PC) from molecular CO2 under mild reaction conditions. In the actual synthesis, the alkylene halohydrins such as alkylene chloro- or bromo or iodohydrin and organic superbase, 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) reacted equivalently with CO2 at room temperature. The syntheses of cyclic carbonates were performed in DMSO as a solvent. Both 1,2 and 1,3 halohydrin precursors were converted into cyclic carbonates except 2-bromo- and iodoethanol, which were reacted equivalently with DBU through n-alkylation and formed corresponding n-alkylated DBU salts instead of forming cyclic carbonates. NMR analysis was used to identify the reaction components in the reaction mixture whereas this technique was also helpful in terms of understanding the reaction mechanism of cyclic carbonate formation. The mechanistic study based on the NMR analysis studies confirmed that prior to the formation of cyclic carbonate, a switchable ionic liquid (SIL) formed in situ from alkylene chlorohydrin, DBU and CO2. As a representative study, the synthesis of cyclic carbonates from 1,2 chlorohydrins was demonstrated where the synthesis was carried out using chlorohydrin as a solvent as well as a reagent. In this case, alkylene chlorohydrin as a solvent not only replaced DMSO in the synthesis but also facilitated an efficient separation of the reaction components from the reaction mixture. The EC or PC, [DBUH][Cl] as well as an excess of the alkylene chlorhydrin were separated from each other following solvent extraction and distillation approaches. In this process, with the applied reaction conditions, >90% yields of EC and PC were achieved. Meanwhile, DBU was recovered from in situ formed [DBUH][Cl] by using NaCl saturated alkaline solution. Most importantly here, we developed a metal free, industrially feasible CO2 capture and utilization approach to obtain EC and PC under mild reaction conditions.

  • 64. Krupinska, Karolina
    et al.
    Geladi, Paul
    Vikholm-Lundin, Inger
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Detection of low levels of Escherichia coli by electrochemical impedance spectroscopy and singular value decomposition2017In: Chemometrics and Intelligent Laboratory Systems, ISSN 0169-7439, E-ISSN 1873-3239, Vol. 163, p. 49-54Article in journal (Refereed)
    Abstract [en]

    The first steps are reported in the development of a new ultrasensitive electrochemical biosensor for detection of Escherichia coli (E. coli) in water. Two gold electrodes in a sandwich flow-cell were modified with E. coli polyclonal antibody and exposed to three different concentrations of E. coli. Electrochemical Impedance Spectroscopy was used in combination with Singular Value Decompostion of the complex numbers to monitor the interactions at the electrode surfaces. A linear regression line in the concentration range 10-1000 CFU⁎ml-1 was obtained without use of redox probes or metal nanoparticles for signal amplification.

  • 65.
    Kussak, Anders
    Umeå University, Faculty of Science and Technology, Department of Chemistry. National Institute of Occupational Health, Analytical Chemistry Division, Umeå, Sweden.
    Development of methods for determining aflatoxins in biological material1995Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, it is shown how aflatoxins can be determined in biological material. The thesis is a summary of five papers.

    Aflatoxins are carcinogenic mycotoxins produced by Aspergillus moulds. Methods were developed for the determination of aflatoxins in samples of airborne dust and human urine collected at feed factories. For the dust samples from such agricultural products as copra, cotton seed and maize, methods were developed for the determination of aflatoxins B1, B2, G1 and G2. For urine samples, methods were developed for analysing the four aflatoxins above that naturally occur in dust, and the metabolites aflatoxins M1 and Q1.

    Sample preparation of dust samples included solvent extraction, filtration and immunoaffinity column extraction. Urine samples were cleaned up using immunoaffinity column extraction or solid-phase extraction using ethyl bonded-phase columns. All extractions with these columns were automated by means of a laboratory robot.

    Reversed-phase liquid chromatography was used to separate the aflatoxins in the cleaned-up extracts. Detection was performed by fluorescence after post-column derivatization by addition of bromine. Parameters for the derivatization were studied using factorial designs. To confirm the identity of aflatoxins in naturally contaminated airborne dust samples and spiked urine, liquid chromatography was combined with electrospray mass spectrometry.

    The detection limits of the aflatoxins in dust samples were in the range 1.8-3.1 ng/g in 10-mg dust samples using fluorescence detection. Aflatoxins were determined in spiked urine down to the 6.8-18 pg/ml level. In naturally contaminated dust of copra and cotton seed, aflatoxins were detected with a content of 9-50 pg/mg of aflatoxin Bi. No aflatoxins could be detected in any urine sample obtained from feed factory workers that were less than 6.8 pg/ml of aflatoxins B1, B2, G1 and G2 and less than 18 pg/ml of aflatoxins M1 and Q1.

  • 66.
    Lambertsson, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Mercury species transformations in marine and biological systems studied by isotope dilution mass spectrometry and stable isotope tracers2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on the implementation of species-specific isotope dilution (SSID) methodology and stable isotope tracers to determine mercury species occurrence and transformation processes in-situ and during sample treatment. Isotope enriched tracers of methyl-, ethyl- and inorganic mercury were synthesised and applied in different combinations to marine and biological samples. Experimental results were obtained using gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS).

    Mercury methylation and methylmercury demethylation processes in surface sediments were studied in the brackish Öre River estuary, Bothnian Bay. Uni- and multivariate data evaluation identified the organic material content and mercury methylation potential in the sediments as important factors controlling incipient methylmercury levels. Mercury species distribution in mice treated with the pharmaceutical preservative Thimerosal (ethylmercurithiosalicylate) was studied. The ethylmercury moiety of Thimerosal was observed to rapidly convert to inorganic mercury in the mice during the treatment period as well as during sample treatment, hence necessitating SSID methodology for accurate ethylmercury determinations in biological samples.

    To facilitate the introduction of SSID as a routine quantitative method in mercury speciation, a methylmercury isotopic certified reference material (ICRM) was produced. Prior to certification, the stability of the material was examined in conventional and isochronous stability studies spanning 12 months, which permitted uncertainty estimation of the methylmercury amount content for two years of shelf-life.

    Finally, a field-adapted SSID method for methylmercury determinations in natural water samples was developed. The proposed analytical protocol significantly simplified sample storage- and treatment procedures without sacrifices in analytical accuracy.

  • 67. LARSSON, H
    ELLIPSOMETRIC DETERMINATIONS OF THE THICKNESSES OF DRY AND ELECTROLYTE-IMMERSED POLY(4-VINYLPYRIDINE) FILMS CONTAINING COORDINATED LIGHT-ABSORBING [OS(BPY)2PVPCL]2+/+ REDOX GROUPS1994In: JOURNAL OF ELECTROANALYTICAL CHEMISTRY, ISSN 1572-6657, Vol. 365, no 1-2, p. 229-237Article in journal (Refereed)
    Abstract [en]

    Ellipsometry has been used to measure the dimensions of quaternized poly(4-vinylpyridine) films containing [Os(bpy)2pvpCl]2+/+ redox groups on glassy carbon electrodes. Film thicknesses and complex refractive indices were deduced using molar absorptivities obtained from photometry or a combination of photometry and cyclic voltammetry. The precision in the film thicknesses was estimated using data obtained from thick and thin films with the same polymer + redox group compositions and from data recorded at 60-degrees and 70-degrees angles of incidence of 633 nm laser light. The effects of errors in the experimentally determined molar absorptivity of the redox groups on film thickness were also assessed. The results of this study suggest that reliable thicknesses can be obtained for both dry and electrolyte-swollen films, and that the presence of light-absorbing redox groups within coatings such as these presents no real obstacle for ellipsometric determinations.

  • 68.
    LARSSON, H
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    LINDHOLM, B
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    SHARP, M
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    ELECTRON-TRANSPORT IN QUATERNIZED POLY(4-VINYLPYRIDINE) FILMS CONTAINING PENTACYANOFERRATE(II/III) ON ELECTRODES - THE INFLUENCE OF THE BINDING TYPE OF THE ELECTROACTIVE COMPLEX1992In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 336, no 1-2, p. 263-279Article in journal (Refereed)
    Abstract [en]

    This study is an attempt to investigate how charge transport in thin redox polymer films spin-coated onto glassy carbon electrode surfaces is affected by the way in which the electroactive group is bound to the polymeric matrix. Two different redox polymers based on methylated and cross-linked poly(4-vinylpyridine) and pentacyanoferrate(II/III) have been synthesized. In the first case, an anionic complex formed by coordinating pyridine to pentacyanoferrate(II) was electrostatically bound to the methylated pyridine groups in the polymer matrix. In the other case, pentacyanoferroate(II) was coordinated directly to unmethylated pyridine groups in the partly methylated polymer film. The film thicknesses were estimated with ellipsometric measurements. Their electrochemical characteristics were investigated using cyclic voltammetry, chronocoulometry and impedance spectroscopy. The apparent charge-transport diffusion coefficient D(app) was almost two orders of magnitude greater in the ion-exchange polymer than in the redox polymer with coordinatively bound electroactive groups. The temperature dependence of D(app) was evaluated using Arrhenius plots.

  • 69.
    LARSSON, H
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    SHARP, M
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    CHARGE PROPAGATION IN [OS(BYP)(2)(PVP)(X)CL]CL POLYMERS - AN EXAMPLE OF MEAN-FIELD BEHAVIOR IN A SYSTEM WITH CONSTRAINED DIFFUSION OF REDOX SITES1995In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 381, no 1-2, p. 133-142Article in journal (Refereed)
    Abstract [en]

    Chronocoulometry and impedance spectroscopy were used to study the dynamics of charge transport in a series of methylated [Os(bpy)(2)(PVP)(x)Cl]Cl polymers (PVP = poly(4-vinylpyridine); bpy = 2,2'-bipyridine; 5 less than or equal to x less than or equal to 40) which were deposited as thin firms on glassy carbon electrodes. Apparent charge propagation diffusion coefficients D-app were of the order of 10(-8) cm(2) s(-1) and were approximately linearly dependent on the total concentration of redox sites but independent of the ratio of oxidized to reduced centres present in a particular coating. Attempts were made to explain these observations in terms of a recent theory of charge transport appropriate for systems in which the redox sites are permanently attached to the polymer chains. It was found that the concentration dependence and magnitude of D-app could be explained satisfactorily by a mean field model of charge propagation.

  • 70.
    Larsson, Tom
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Instrumental and methodological developments for isotope dilution analysis of gaseous mercury species2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with instrumental and methodological developments for speciation analysis of gaseous mercury (Hg(g)), based on isotope dilution analysis (IDA). The studied species include Hg0, (CH3)2Hg, CH3HgX and HgX2 (where X symbolises a negatively charged counter ion in the form of a halide or hydroxyl ion). Gas chromatography hyphenated with inductively coupled plasma mass spectrometry (GC-ICPMS) was used for separation and detection of Hg(g) species. Permeation tubes were used for the generation of gaseous isotopically enriched Hg standards (tracers). These tracers were continuously added to the sample gas stream during sampling of Hg(g). A mobile prototype apparatus incorporating both the permeation source and a sampling unit for collection of Hg(g) was developed and used for this purpose. Hg(g) species were pre-concentrated on Tenax TA and / or Carbotrap solid adsorbents. Au-Pt was used for pre-concentration of total Hg(g), either as the primary medium, or as backup. Collected species were eluted from these media and introduced to the instrument by thermal desorption.

    Various degrees of species transformations, as well as losses of analyte during pre-concentration and elution, were found to occur for both Tenax TA and Carbotrap. The performance characteristics of these media were shown to be species specific, as well as matrix dependent. The development of an on-line derivatisation procedure allowed for minimised species transformations, as well as reduced adsorption and memory effects of ionic Hg(g) species within the analytical system. In conclusion, IDA provides an important tool for identification, minimisation and correction of the above mentioned analytical problems. Furthermore, it offers significant advantages with respect to quality assurance, compared to conventional techniques, both when it comes to rational development of new methodology, as well as for continuous validation of existing procedures.

    The developed methodology for speciation analysis of Hg(g) has been tested in various applications, including the determination of Hg(g) species concentrations in ambient air (both in and outdoor) and in the head space of sediment microcosms. Hg(g) species were formed in the sediments as a result of naturally occurring redox and methylation processes, after addition of an isotope enriched aqueous Hg(II) precursor. The methodology has also been used for assessing the risk of occupational exposure to Hg(g) species during remediation of a Hg contaminated soil and for studying Hg0(g) transport and Au-Pt pre-concentration characteristics in natural gases. Hg0 was used as the model species in the latter experiments, since it is believed to be the dominating form of Hg(g) in natural gas. The results indicate that the occurrence of H2S can cause temperature dependent adsorption and memory effects of Hg0(g) in the presence of stainless steel, thereby providing a plausible explanation to the variability of results for sour gases occasionally observed in the field. Hg0(g) has demonstrated overall high recovery during collection on Au-Pt tubes for all gases tested in this thesis. Recent (unpublished) results however indicate that there are potential species specific and matrix dependent effects associated with the Au-Pt based pre-concentration of Hg(g) in natural gases.

  • 71.
    Larsson, William
    Umeå University, Faculty of Science and Technology, Chemistry.
    New approaches to moisture determination in complex matrices based on the Karl Fischer Reaction in methanolic and non-alcoholic media2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Moisture determination is of great importance in the production and use of many substances. For example, the moisture content can affect the efficiency of a chemical reaction or determine the shelf life of pharmaceuticals or foods. The standard method for moisture determination is Karl Fischer (KF) titration, based on either volumetry or coulometry. This thesis concerns new approaches to trace determination in complex sample matrices and is focused on oils and substances that interfere with alcoholic KF reagents.

    Moisture is frequently separated from oil matrices before titration by means of evaporation techniques. In connection with the preparation of new reference materials for moisture in oil, the National Institute of Standards and Technology (NIST) questioned the efficiency of such evaporation techniques. NIST claimed that some of the moisture was sequestered in the oil phase and that it could only be released and detected by using a modified volumetric KF method with a reagent containing at least 65% chloroform. In this thesis, an alternative KF method that meets the proposed requirement for a complete dissolution of the oil sample is presented. With this method it is shown that there is no reason to question the efficiency of the evaporation techniques and that the criticized volumetric method used by NIST is biased high.

    Ever since its introduction diaphragm-free coulometry has gained popularity due to its ease of use, with a single reagent and short conditioning times. Trace determination with this technique sets great demands on the reagent due to the resulting low current densities at the generator cathode. The performance of several commercial reagents is evaluated under such unfavorable conditions and critical titration parameters are identified. It is also shown that decanol has a favorable effect on the cathode process when using reagents modified with xylene according to standard methods for moisture determination in oils.

    For samples that are incompatible with the alcohol component in ordinary KF reagent a new reagent based on N-methylformamide is presented. It is shown that is works well for determinations of moisture in a conductive salt used in lithium-ion batteries. The concept of alcohol-free KF reagents is taken a step further in a systematic investigation, also including formamide and dimethylformamide. Advantages and disadvantages with these solvents are discussed and possible reaction paths are surveyed. It is shown that the position of the sulfur dioxide/hydrogen sulfite equilibrium is the main explanation for the large differences in the KF reaction rates in these solvents.

  • 72.
    Le, Tinh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Determination of Cisplatin using Hydrophilic Interaction Liquid Chromatography (HILIC) Coupled with Inductively Coupled Plasma Mass Spectrometry (ICP-MS): A Study on Cisplatin’s Retention Mechanisms in HILIC and Uptake and Intracellular Decay Kinetics in in-vitro Grown Cells2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Cisplatin (cis-diamminedichloroplatinum(II), CDDP) is widely used for the treatment of several solid tumors. The antitumor property of cisplatin is generally proved that the covalent binding of cisplatin to DNA distorts the DNA structure, which leads to the death of the cancer cells. The obstacle for chemotherapy is that tumors can acquire resistance to cisplatin and induce the severe side effects associated with cisplatin treatment. How cisplatin enters the cells and metabolizes in cytoplasm is not completely elucidated. The purpose of this project was to study the kinetics of cellular uptake of cisplatin and decay of intracellular cisplatin in in-vitro grown cells. Another aim was to investigate the retention mechanism of cisplatin on a zwitter-ionic hydrophilic interaction liquid chromatography (ZIC®-HILIC) column.

    HILIC coupled on-line to inductively coupled plasma mass spectrometry was applied to separate and quantify cisplatin content in cell lysates from malignant melanoma cells exposed to cisplatin. The cells were lysed by using a ceramic bead method.

    Both sensitive and resistant cells gained the maximum total platinum uptake after 60 minutes. The sensitive cells accumulate more total-Pt but not more free cisplatin than resistant cells.The half-life of cisplatin in resistant cells exposed to 20 and 100μM cisplatin was found to be 17 and 14 minutes, respectively. The results also indicated that the interaction of cisplatin with ZIC-HILIC stationary phase was likely to be hydrogen bonding interaction.

  • 73.
    Liem-Nguyen, Van
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Determination of mercury chemical speciation in the presence of low molecular mass thiols and its importance for mercury methylation2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Methylmercury (MeHg) is a neurotoxic compound that threatens the well-being of humans and wildlife. It is formed through the methylation of inorganic mercury (HgII) under suboxic/anoxic conditions in soils, sediment and waters. The chemical speciation of HgII, including specific HgII species in aqueous and solid/adsorbed phases, plays a key role in MeHg formation. Chemical forms of HgII which have been reported to be available for uptake in methylating bacteria include neutral HgII–sulfide complexes, HgII complexes with specific low molecular mass (LMM) thiols, and nanoparticulate HgS(s). Accurate determination of the chemical speciation of HgII is thus crucial when elucidating the mechanism of MeHg formation. The concentration of HgII–LMM thiols complexes is predicted to be extremely low (sub fM range). Current analytical methods do not allow direct quantification of HgII complexes due to the very low concentration of these complexes, and therefore determination rely on thermodynamic modeling. Accurate stability constants for HgII–LMM thiols complexes and quantification of LMM thiol ligands in environments are thus required to precisely determine the concentration of such complexes.

    In this thesis, a novel analytical method was developed based on online pre-concentration coupled with liquid chromatography tandem mass spectrometry to determine the concentration of 16 LMM thiols (Paper I). This method was successful in detecting 8 LMM thiols in boreal wetland porewaters, with mercaptoacetic acid and cysteine being the most abundant. The total concentration of individual detected LMM thiols ranged from sub nM (LOD=0.1 nM) to 77 nM. Moreover, the stability constant (β2) for HgII complexes with 15 LMM thiols were directly determined for the first time by competing ligand exchange experiments combined with liquid chromatography ICPMS analysis (Paper II). Values of log β2 for the reaction Hg2+ + 2LMM-RS- = Hg(LMM-RS)2 ranged from 34.6 for. Based on the determined constants of Hg(LMM-RS)2 complexes and state-of-the-art constants from literature for other HgII complexes, we established comprehensive thermodynamic speciation models for MeHg and HgII in boreal wetlands (Paper III). The speciation of HgII was coupled with the HgII methylation rate constant (km) determined with different enriched Hg isotope tracers (Paper IV). There was a good correlation (R2=0.88) between the km determined by a HgII(aq) tracer added as Hg(NO3)2 with high bioavailability and a tracer where HgII was bond to thiol groups in natural organic matter (HgII-NOM(ads)) and has a lower bioavailability. The HgII(aq) tracer was consistently methylated at 5 times higher rate than the HgII-NOM(ads) tracer. A good correlation was observed between the concentration of biologically produced LMM thiols and km in the boreal wetlands. In a mesocosm study of estuarine sediment-brackish water systems, increased concentration of phytoplankton chlorophyll α due to macro nutrient additions led to an increase in HgII methylation rate of the HgII(aq) but not of the HgII-NOM(ads) tracer or ambient HgII species (Paper V). Furthermore, simulated newly deposited HgII species from atmospheric and terrestrial sources were exhibited significantly higher HgII methylation rates when compared with simulated aged sediment HgII pools. Through the development and adoption of novel analytical methods, this thesis reveals the significance of LMM thiols in Hg biogeochemistry by precise determination of HgII–LMM thiol complexes in natural environmental systems.

  • 74.
    Liem-Nguyen, Van
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bouchet, Sylvain
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Determination of Sub-Nanomolar Levels of Low Molecular Mass Thiols in Natural Waters by Liquid Chromatography Tandem Mass Spectrometry after Derivatization with p‑(Hydroxymercuri) Benzoate and Online Preconcentration2015In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 87, no 2, p. 1089-1096Article in journal (Refereed)
    Abstract [en]

    Low molecular mass (LMM) thiols is a diverse group of compounds, which play several important roles in aquatic ecosystems, even though they typically occur at low concentrations. Comprehensive studies of LMM thiols in natural waters have so far been hampered by selectivity and limit of detection constraints of previous analytical methods. Here, we describe a selective and robust method for the quantification of 16 LMM thiols in natural waters. Thiols were derivatized with 4-(hydroxymercuri)benzoate (PHMB) and preconcentrated online by solid-phase extraction (SPE) before separation by liquid chromatography and determination by electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Their quantification was performed by selective reaction monitoring (SRM), while the presence of a product ion atm/z 355, specific for thiols and common for the investigated compounds, also allows to screen samples for unknown thiols by a precursor ion scan approach. The robustness of the method was validated for aqueous matrices with different pH, sulfide, and dissolved organic carbon (DOC) concentrations. The limits of detection for the thiols were in the sub-nanomolar range (0.06–0.5 nM) and the methodology allowed determination of both reduced and total thiol concentrations (using tris(2-carboxyethyl)phosphine (TCEP) as reducing agent). Six thiols (mercaptoacetic acid, cysteine, homocysteine, N-acetyl-cysteine, mercaptoethane-sulfonate, and glutathione) were detected with total concentrations of 7–153 nM in boreal lake or wetland pore waters while four thiols (mercaptoacetic acid, cysteine, homocysteine, and N-acetyl-cysteine) were detected in their reduced form at concentrations of 5–80 nM.

  • 75.
    Liem-Nguyen, Van
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. School of Science and Technology, Örebro University, SE-70281, Örebro, Sweden.
    Huynh, Khoa
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gallampois, Christine
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Determination of picomolar concentrations of thiol compounds in natural waters and biological samples by tandem mass spectrometry with online preconcentration and isotope-labeling derivatization2019In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 1067, p. 71-78Article in journal (Refereed)
    Abstract [en]

    We present a sensitive, selective and robust method for the determination of 14 thiol compounds in aqueous samples. Thiols were derivatized with omega-bromoacetonylquinolinium bromide (BQB) and its deuterium labeled equivalent D7-ω-bromoacetonylquinolinium bromide (D7). Derivatized thiols were preconcentrated by online solid-phase extraction (SPE) followed by liquid chromatography separation and electrospray ionization tandem mass spectrometry determination (SPE/LC-ESI-MS/MS). The robustness of the method was validated for wide ranges in pH, salinity, and concentrations of sulfide and dissolved organic carbon (DOC) to cover contrasting natural water types. The limits of detection (LODs) for the thiols were 3.1-66 pM. Between 6 and 14 of the thiols were detected in different natural sample types at variable concentrations: boreal wetland porewater (0.7-51 nM), estuarine sediment porewater (50 pM-11 nM), coastal sea water (60 pM-16 nM), and sulfate reducing bacterium cultures (80 pM-4 nM). MS/MS fragmentation of the compounds produces two pairs of common product ions, m/z 130.2/137.1 and 218.1/225.1, which enables scanning for unknown thiols in precursor ion scan mode. Using this approach, we identified cysteine, mercaptoacetic acid, N-acetyl-L-cysteine and sulfurothioic S-acid in boreal wetland porewater. The performance of the developed method sets a new state of the art for the determination of thiol compounds in environmental and biological samples.

  • 76.
    Liem-Nguyen, Van
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mercury chemical speciation and biological production of low molecular mass thiols in control of methylmercury formation in boreal wetlandsManuscript (preprint) (Other academic)
  • 77.
    Liem-Nguyen, Van
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Thermodynamic modelling of the chemical speciation of mercury and methylmercury under sulfidic conditions in boreal wetland soilsManuscript (preprint) (Other academic)
  • 78.
    Liem-Nguyen, Van
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Nam, Kwangho
    Erik, Björn
    Stability constants for mercury (II) complexes with low molecular mass thiols as determined by competing ligand exchange and liquid chromatography inductively coupled plasma mass spectrometryManuscript (preprint) (Other academic)
  • 79.
    Limé, Fredrik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Synthesis and modification of monodisperse polymer particles for chromatography2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Liquid chromatography is an analytical technique that is constantly facing new challenges in the separation of small molecules and large biomacromolecules. Recently the development of ultra high pressure liquid chromatography has increased the demand on sturdy particles as stationary phase. At the same time the particle size has decreased to sub-2 µm and packed into shorter analytical columns. This thesis deals with the development of new ways of preparing particulate polymer materials using divinylbenzene (DVB) as crosslinker. It includes a novel procedure for synthesizing monodisperse polymer particles by photoinitiated precipitation polymerization. A 150 W short arc xenon lamp was used to initiate the polymerizations. The synthesized particles are monodisperse and have an average particle size ranging from 1.5 to 4 μm depending on reaction conditions and have subsequently been used as grafting templates. The surface of DVB particles contains residual vinyl groups that serve as anchoring points for further functionalization via a variety of grafting schemes. Copolymerization with incorporation of 2,3-epoxypropyl methacrylate yielded pendant oxirane groups on the particle surface. Atom transfer radical polymerization (ATRP) was used to graft methacrylates from the surface resulting in a core-shell type material. A “grafting to” scheme was used to attach pre-made sulfopropyl methacrylate telomers onto particles containing oxirane rings.

  • 80.
    Lindberg, Richard H.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Östman, Marcus
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Olofsson, Ulrika
    Grabic, Roman
    Fick, Jerker
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Occurrence and behaviour of 105 active pharmaceutical ingredients in sewage waters of a municipal sewer collection system2014In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 58, p. 221-229Article in journal (Refereed)
    Abstract [en]

    The concentrations and behaviour of 105 different active pharmaceutical ingredients (APIs) in the aqueous phase of sewage water within a municipal sewer collection system have been investigated. Sewage water samples were gathered from seven pump stations (one of which was located within a university hospital) and from sewage water treatment influent and effluent. The targeted APIs were quantified using a multi-residue method based on online solid phase extraction liquid chromatography tandem mass spectrometry. The method was thoroughly validated and complies with EU regulations on sample handling, limits of quantification, quality control and selectivity. 51 APIs, including antibiotics, antidepressants, hypertension drugs, analgesics, NSAIDs and psycholeptics, were found frequently within the sewer collection system. API concentrations and mass flows were evaluated in terms of their frequency of detection, daily variation, median/minimum/maximum/average concentrations, demographic dissimilarities, removal efficiencies, and mass flow profiles relative to municipal sales data. Our results suggest that some APIs are removed from, or introduced to, the aqueous phase of sewage waters within the studied municipal collection system.

  • 81.
    Liu, Mingquan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Torsetnes, Silje Bøen
    Wierzbicka, Celina
    Jensen, Ole Nørregaard
    Sellergren, Börje
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Selective Enrichment of Phosphorylated Peptides by Monolithic Polymers Surface Imprinted with bis-Imidazolium Moieties by UV-Initiated Cryopolymerization2019In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 91, no 15, p. 10188-10196Article in journal (Refereed)
    Abstract [en]

    Reversible protein phosphorylation on serine, threonine, and tyrosine residues is essential for fast, specific, and accurate signal transduction in cells. Up to now, the identification and quantification of phosphorylated amino acids, peptides, and proteins continue to be one of the significant challenges in contemporary bioanalytical research. In this paper, a series of surface grafted monoliths in the capillary format targeting phosphorylated serine has been prepared by first synthesizing a monolithic core substrate material based on trimethylolpropane trimethacrylate, onto which a thin surface-imprinted layer was established by oriented photografting of a variety of mono- and bis-imidazolium host monomers at subzero temperature, using six different continuous or pulsed UV light sources. The imprinted monolith capillaries were evaluated in a capillary liquid chromatographic system connected to a mass spectrometer in order to test the specific retention of phosphorylated peptides. Site-specific recognition selectivity and specificity for phosphorylated serine was demonstrated when separating amino acids and peptides, proving that the optimized materials could be used as novel trapping media in affinity-based phosphoproteomic analysis.

  • 82.
    Lukkari, Ingrid
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Flow injection systems for process analytical chemistry1995Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Flow injection systems have great potential for sample handling and analysis in process analytical chemistry. The flexibility and versatility of flow injection manifolds can he utilized in specific applications of sample conditioning and analysis. An overview of various flow injection methods, including flow reversals, double injection, and sequential injection is given, as well as different clean-up methods, such as gas diffusion, solid phase extraction, dialysis, and solvent extraction. Calibration techniques, such as single standard and multivariate calibration are also discussed. In addition, different aspects of process analytical chemistry, in particular sampling and sample handling, are discussed.

    The papers in this thesis describe a number of flow systems, where gradient-, gas diffusion-, and solid phase extraction- methodologies are applied, all of which have potential use in process analytical chemistry. Paper I is focused on multicomponent analysis of mixtures of organic acids by mathematically extracting information from complex spectra. The selectivity is improved by generating pH-gradients in the flow system. In paper II, the methodology of sensor injection is described and electrochemical and spectroscopic sensors are implemented in a sequential injection system. The method is illustrated by using pH sensors and a glucose electrode. Ammonia and ammonium ions are determined on-line to a bioprocess by gas diffusion in paper III. The benefit of frequent re-calibrations and in-line cleaning sequences are demonstrated. Finally a method for on-line determination of o-diphenols in the kraft process has been developed (paper IV). The o-diphenols are isolated from black liquor samples by solid phase extraction and thereafter transferred to a high performance liquid chromatography system for separation and quantification.

  • 83.
    Lundgren, Gillis
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Temperature controlled heating of the graphite tube atomizer for flameless atomic absorption spectroscopy: with special application to the determination of trace metals in biological materials1975Doctoral thesis, comprehensive summary (Other academic)
  • 84.
    Lundstedt, Staffan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bandowe, B. A. M.
    Wilcke, W.
    Boll, E.
    Christensen, J. H.
    Vila, J.
    Grifoll, M.
    Faure, P.
    Biache, C.
    Lorgeoux, C.
    Larsson, M.
    Frech Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ivarsson, P.
    Ricci, M.
    First intercomparison study on the analysis of oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) and nitrogen heterocyclic polycyclic aromatic compounds (N-PACs) in contaminated soil2014In: TrAC. Trends in analytical chemistry, ISSN 0165-9936, E-ISSN 1879-3142, Vol. 57, p. 83-92Article, review/survey (Refereed)
    Abstract [en]

    Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) and nitrogen heterocyclic polycyclic aromatic compounds (N-PACs) are toxic, highly leachable and often abundant at sites that are also contaminated with PAHs. However, due to lack of regulations and standardized methods for their analysis, they are seldom included in monitoring and risk-assessment programs. This intercomparison study constitutes an important step in the harmonization of the analytical methods currently used, and may also be considered a first step towards the certification of reference materials for these compounds. The results showed that the participants were able to determine oxy-PAHs with accuracy similar to PAHs, with average determined mass fractions agreeing well with the known levels in a spiked soil and acceptable inter- and intra-laboratory precisions for all soils analyzed. For the N-PACs, the results were less satisfactory, and have to be improved by using analytical methods more specifically optimized for these compounds.

  • 85.
    Löfgren, Mikael
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Mätning av viskositet på stärkelse2015Independent thesis Basic level (university diploma), 5 credits / 7,5 HE creditsStudent thesis
    Abstract [en]

    Starch is used in papermaking to increase the strength properties of the paper. The starch can for various reasons degrade and become worse, primarily due to bacteria. This can lead to poor paper quality and in worst case to rejects of the final product.

    To investigate whether the starch has become infested with bacteria, a bacteria culture can be made. The downside of this is that it takes very long time before any results can be seen. Another effect of the bacteria is that the viscosity of the starch gets lower, i.e. the liquid becomes less viscous. This is a parameter that can be measured with a viscometer.

    The aim is to develop a new measurement standard for detecting bacterial attacks, where the main advantage is that the method provides a quick and reliable response, thus reducing the reaction time to counteract the bacteria.

    The goal of the project is to measure the viscosity of starch cooked in the mill and starch cooked in the lab and by doing so, start to build up a database of values to validate the viscometer.

    The work has been carried out in the laboratory at Tech Center at Smurfit Kappa, Piteå. An important discovery was made that the pH may be low but it does not necessarily have to be a bacterial attack.

    The work is limited a lot by the time period of five weeks and it is possible that more measurements would produce a different result.

    The measurements made suggest that it is possible to measure the viscosity of the starch from one day to another and that the parameter will remain unchanged as long as the concentration is constant.

    The work of collecting data from lab cooked starch and starch cooked in the jet boiler at the mill is the beginning to validate the method. More measurements will be carried out in order to keep statistics of the viscosity. Factors like temperature and concentration’s effects on the viscosity will be evaluated. The goal is to correct for these in order to be able to correlate data to a bacterial infestation. If successful, the next step is to implement the method as a standard in the laboratory.  

  • 86.
    Löfstedt, Tommy
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    OnPLS—a novel multiblock method for the modelling of predictive and orthogonal variation2011In: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, Vol. 25, no 8, p. 441-455Article in journal (Refereed)
    Abstract [en]

    This paper presents a new multiblock analysis method called OnPLS, a general extension of O2PLS to the multiblock case. The proposed method is equivalent to O2PLS in cases involving only two matrices, but generalises to cases involving more than two matrices without giving preference to any particular matrix: the method is fully symmetric. OnPLS extracts a minimal number of globally predictive components that exhibit maximal covariance and correlation. Furthermore, the method can be used to study orthogonal variation, i.e. local phenomena captured in the data that are specific to individual combinations of matrices or to individual matrices. The method's utility was demonstrated by its application to three synthetic data sets. It was shown that OnPLS affords a reduced number of globally predictive components and increased intercorrelations of scores, and that it greatly facilitates interpretation of the predictive model.

  • 87. McAlpin, J. Gregory
    et al.
    Stich, Troy A.
    Ohlin, C. Andre
    Surendranath, Yogesh
    Nocera, Daniel G.
    Casey, William H.
    Britt, R. David
    Electronic Structure Description of a [Co(III)(3)Co(IV)O-4] Cluster: A Model for the Paramagnetic Intermediate in Cobalt-Catalyzed Water Oxidation2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 39, p. 15444-15452Article in journal (Refereed)
    Abstract [en]

    Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co4O4(C5H5N)(4)(CH3CO2)(4)](+) (1(+)), a cobalt tetramer with total electron spin S = 1/2 and formal cobalt oxidation states III, III, III, and IV. The cuboidal arrangement of its cobalt and oxygen atoms is similar to that of proposed structures for the molecular cobaltate clusters of the cobalt-phosphate (Co-Pi) water-oxidizing catalyst. The Davies electron-nuclear double resonance (ENDOR) spectrum is well-modeled using a single class of hyperfine-coupled Co-59 nuclei with a modestly strong interaction (principal elements of the hyperfine tensor are equal to [-20(+/- 2), 77(+/- 1), -5(+/- 15)] MHz). Mims H-1 ENDOR spectra of 1(+) with selectively deuterated pyridine ligands confirm that the amount of unpaired spin on the cobalt-bonding partner is significantly reduced from unity. Multifrequency N-14 ESEEM spectra (acquired at 9.5 and 34.0 GHz) indicate that four nearly equivalent nitrogen nuclei are coupled to the electron spin. Cumulatively, our EPR spectroscopic findings indicate that the unpaired spin is delocalized almost equally across the eight core atoms, a finding corroborated by results from DFT calculations. Each octahedrally coordinated cobalt ion is forced into a low-spin electron configuration by the anionic oxo and carboxylato ligands, and a fractional electron hole is localized on each metal center in a Co 3d(xz,yz)-based molecular orbital for this essentially [Co4+3.125O4] system. Comparing the EPR spectrum of 1(+) with that of the catalyst film allows us to draw conclusions about the electronic structure of this water-oxidation catalyst.

  • 88. Moilanen, Antero
    et al.
    Lehtinen, Jere
    Kurkela, Minna
    Muhola, Mirja
    Tuomi, Sanna
    Carlsson, Per
    Öhman, Marcus
    Güell, Berta Matas
    Sandquist, Judit
    Lundgren, Joakim
    Andersson, Jim
    Umeki, Kentaro
    Ma, Charlie
    Kurkela, Esa
    Wiinikka, Henrik
    Wang, Liang
    Backman, Rainer
    Biomass gasification fundamentals to support the development of BTL in forest industry2015Report (Other academic)
  • 89. Moreno-Guzman, Maria
    et al.
    Garcia-Carmona, Laura
    Molinero-Fernandez, Agueda
    Cava, Felipe
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Lopez Gil, Miguel Angel
    Escarpa, Alberto
    Bi-enzymatic biosensor for on-site, fast and reliable electrochemical detection of relevant D-amino acids in bacterial samples2017In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 242, p. 95-101Article in journal (Refereed)
    Abstract [en]

    In this work, a bi-enzymatic biosensor allowed the total content of D-amino acids (DAAs) determination in highly relevant matrices involving bacteria. The strategy is based on the unique coimmobilization of D-amino acid oxidase (DAAO) and horseradish peroxidase (HRP) enzymes onto a multi-walled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs) modified screen-printed electrode (SPCE). The greater amount of AuNPs deposited and hence the greater loading of both enzymes was observed when they were deposited after the activation of the carboxylated MWCNTs with EDC/Sulfo-NHS chemistry. These platforms provided a fast (300s) and selective quantification of DAAs with excellent precision (RSD < 5%) and accuracy (Recoveries 100-104%) in bacterial samples. Collectively, the electrochemical bi-enzymatic biosensor become an universal, fast, sensitive and easy-to-use approach to determine total content of DAAs in complex matrices.

  • 90. Newton, Seth
    et al.
    Bidleman, Terry
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bergknut, Magnus
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Racine, Jacinthe
    Laudon, Hjalmar
    Giesler, Reiner
    Wiberg, Karin
    Atmospheric deposition of persistent organic pollutants and chemicals of emerging concern at two sites in northern Sweden2014In: Environmental science: processes & impacts, ISSN 2050-7887, Vol. 16, no 2, p. 298-305Article in journal (Refereed)
    Abstract [en]

    Bimonthly bulk atmospheric deposition samples (precipitation + dry particle) were taken for one year at an arctic (Abisko, 68 degrees 20' N, 19 degrees 03' E) and a sub-arctic (Krycklan 64 degrees 14' N, 19 degrees 46' E) location in northern Sweden using Amberlite IRA-743 as an absorbent for hydrophobic pollutants. The samples were analyzed by gas chromatography-high resolution mass spectrometry (GC-HRMS) for polychlorinated biphenyls (PCBs), legacy organochlorine pesticides (OCPs = hexachlorocyclohexanes and chlordane-related compounds), polybrominated diphenyl ethers (PBDEs) and emerging chemicals. Higher deposition rates of most compounds were observed at the more northern site despite its receiving less precipitation and being more remote. HCHs and PCBs made up the bulk of the total deposition at both sites. Five emerging chemicals were detected: the current-use pesticides trifluralin and chlorothabnil; and non-BDE flame retardants 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), and Dechlorane Plus (DP). A decrease in the fraction of the anti isomer of DP was observed at the arctic site, indicating isomer-selective degradation or isomerization during long range transport. Air parcel back trajectories revealed a greater influence from air originating over the ocean at the more northern site. The differences in these air sources were reflected in higher Sigma HCH to Sigma PCB ratios compared to the more southern site, as HCHs are related to volatilization from the ocean and Abisko is located <100 km from the Norwegian coast, while PCBs are emitted from continental sources.

  • 91.
    Nguyen, Anh Mai
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    New approaches to preparation of macroporous monoliths for use in liquid chromatography2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High performance liquid chromatography (HPLC) is one of the major techniques in separat-ion sciences. Faster separation and higher efficiency are required to meet ever-growing demands. Despite numerous studies and achievements on improving mass transfer in particulate packings discontinuity seems to be the cornerstone drawback in their development. Macroporous continuous beds or monoliths are therefore a promising alternative to the particle medium. This thesis deals with preparation of new monoliths used as carrier for HPLC. Two different approaches were developed for two polymer systems. One was based on polycondensation of epoxy resins and polyamines which were components of an oil-in-water emulsion. An epoxy resin mixture was dispersed in aqueous polyamine phase with the aid of a surfactant. The other involved a traverse of a ready-made polymer solution around its upper critical solution temperature (UCST). In other words, linear polyamides, non-covalently crosslinked polymers, dissolved in a solvent at temperature higher than their UCST followed by slow cooling to below the critical temperature to precipitate the polymers. Partly re-established hydrogen bonds resulted in the formation of crystallites that interconnected into a network structure. Factors controlling morphology and porosity of final products were investigated. The study also deals with surface modifying for chromatographic applications. Functionalization pathways attempted in the thesis were quaterization of inherent amine of the epoxy-based monoliths and grafting tentacle ion groups via glycidyl methacrylate by atom transfer radical polymerization (ATRP) for ion exchange chromatography (IEC).

  • 92.
    Nguyen, Anh Mai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nordborg, Anna
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Thermally induced dissolution/precipitation: A simple approach for the preparation of Macroporous Monoliths from Linear Aliphatic Polyamides2009In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 32, no 15-16, p. 2619-2628Article in journal (Refereed)
    Abstract [en]

    A versatile way of preparing macroporous monolithic materials from linear aliphatic polyamides is presented. Simply, polyamide pellets were treated in benzyl alcohol (BA) at elevated temperature, causing dissolution by interchain hydrogen bond disruption. Subsequent cooling below the upper critical solution temperature (UCST) resulted in precipitation and partial restoration of the semicrystalline polymer, which is organized into network structures. The final steps were a solvent exchange of BA for methanol, followed by drying to form monolithic entities. A number of polyamides ranging from hydrophilic to hydrophobic were tested and under the experimental conditions, poly(1-aza-2-cycloheptanone (PA6) and (poly-[imino-1,6-hexanediylimino{1,10-dioxo-1,10-decanediyl}] (PA610) yielded entities with macroporous properties that were deemed useful for liquid chromatography. The morphological features and porous properties of the monoliths produced by this dissolution-precipitation procedure were studied by scanning electron microscopy, adsorption/desorption of N2(g) according to the Brunauer-Emmett-Teller (BET) principle, and mercury intrusion porosimetry. Degradation of the polymer backbone was noticeable when the dissolution time was extended and shortening of the polymer chains was confirmed by MALDI-MS, viscosity measurements, X-ray photoelectron spectroscopy (XPS), and potentiometric titration. When the heating was limited to the time it took to dissolve the polymers, mechanically stable monoliths could be obtained. The dissolution/heat treatment time further seemed to be useful for controlling the macroporous morphology.

  • 93.
    Nguyen Van, Dong
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Speciation analysis of butyl- and phenyltin compounds in environmental samples by GC separation and atomic spectrometric detection2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main goal of the work presented in this thesis is to improve the reliability of existing methods for speciation analysis of organotin compounds

    Species-specific isotope dilution (SSID) calibration in combination with gas chromatography – inductively coupled plasma mass spectrometry was used to investigate the transformation of phenyltin species during sample preparation. Isotope-enriched phenyltin species were synthesized from corresponding isotope-enriched tin metals. SSID with a mixture of phenyltin species (PhTs) from one isotope was used to evaluate different extraction procedures for the determination of PhTs in fresh water sediment. Preparative liquid chromatography was used to produce single isotope-enriched phenyltin species making a multi-isotope spike (MI) SSID calibration possible. Different extraction procedures for the analysis of phenyltin species in biological samples were evaluated by applying MI-SSID. Degradation of TPhT and DPhT during sample extraction was observed and quantified. Accurate results were therefore obtained. A sample preparation procedure using mild extraction conditions with reasonable recoveries is described.

    The stability of organotin standards was investigated under different storage conditions. Mono- and diphenyltin were found to be redistributed and degraded during storage in methanol but were stabilized in sodium acetate/ acetic acid. A fast redistribution between monobutyl- and diphenyl tin has been observed and therefore it is therefore recommended that standards be derivatized as soon as possible after butyl- and phenyltin standards are mixed.

    Included in the thesis is also an investigation of the analytical potential of using instrumentation based on atomic absorption spectrometry (AAS) for speciation analysis of organotin compounds. The method was based on gas chromatographic separation, atomization in a quartz tube and detection by line source (LS) AAS and for comparison, by state of the art continuum source (CS) AAS. Analytical performances of CSAAS system were found to be better compared to LSAAS.

  • 94.
    Nguyen Van, Liem
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Intracellular half-life of cisplatin in malignant cells: A kinetic study of the decline rate of intracellular cisplatin concentration in in-vitro grown cells determined by LC-ICP-MS following exposure to clinically relevant cisplatin doses2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Cisplatin is a common cancer therapy substance used against several types of malignant tumors and often shows great efficiency. The most important tumour killing mechanism is believed to be formation of Pt-DNA adducts. It is however a common phenomenon that tumors develop resistance causing inefficient treatment.

    It is generally believed that Pt-DNA adduct formation follows after intracellular “activation” of the drug substances by hydrolysis reactions due to the lower chloride concentration intra- compared to extra-cellular. The kinetics for these activation processes and other potential metabolic reactions for the Pt-drugs in-vivo are virtually unknown.

    The presence of free intracellular cisplatin in in-vitro grown human malignant melanoma cell lines have been shown previously and the aim of this study is to determine the kinetics of decline in intracellular cisplatin concentration in in-vitro grown cells following exposure to clinically relevant cisplatin doses 2, 20 and100μM with 60 minutes exposure time.

    Species were separated on a 2.1 x 150mm, 3.5 μm, 200Å ZIC-HILIC column and detected online by selective platinum (m/z 194 and 195) monitoring using ICP-MS. The system was optimized with respect to detection limit (0.5pg) to be able to use low exposure concentration of cisplatin in the cell incubation experiments. The half life and the kinetic curve were determined by using the incubation time of 0 to 30 minutes in cisplatin free medium. A ceramic bead method was used for cell lysis, and cisplatin, total platinum and total protein concentration were measured in the lysates.

    The, intracellular concentration of cisplatin and total platinum as well as the intracellular half life of cisplatin, were determined in both cisplatin sensitive (T289 wild type) and resistant (T289 DDP) malignant melanoma cells. The half life and total platinum depends on the type of cells and the exposure doses. For sensitive cells, with low exposure doses (2, 20μM), the half life was determined to 12 minutes and with high exposure dose, the half life reduced quickly and was determined to be 6 minutes. For resistant cells, the half life was determined to 16, 14, and10 minutes for 2, 20, and 100μM exposure doses, respectively. The intracellular cisplatin and total platinum in resistant cells were lower than in sensitive cells.

    The reaction order for the metabolism of intracellular cisplatin was also investigated. The decline in cisplatin concentration did not really follow the first or second order reaction. However, for sensitive cells, the reduction seemed to be close to the first order at low exposure doses (2, 20μM) and the second order with the high exposure dose (100μM) and for resistant cells, the reduction of cisplatin seemed to follow the first order in all exposure doses.

  • 95.
    Nguyen Van, Liem
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tollin, Henrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tran Thanh, Tu
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Coupling of a home-made simulated automatic mercury analyzer (AMA254) to a mercury fluorescence detector for total mercury determination in biological samples: -The use of a hydride generator system and atomic absorption spectroscopy to detect mercury in water samples 2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this project we have been working with two different instruments home-made AMA 254 and Hydride Generator. Home-made AMA 254 was coupled to a fluorescence detector. The Hydride Generator was coupled to atomic absorption spectroscopy (AAS), by an optical path.

    Calibration of mass-flow controller by applying a suitable gas in the inlet and a bubbles calibration unit at the outlet. All date was saved by labview program was used

    The first configurations, carrier gas was fed into the middle of the catalyzer tube

    and the gold-trap by a T-shape connector to carry mercury to the detector.

    Condensation of mercury vapour when the gas-stream collided to the silicon walls, at the T-shape connection leads to failing.

    Second configuration, two positioned-switching valve was introduced between the oxygen and argon tanks, allowing only one gas to reach MFC depending on the switching position.

    There are four different parameters memory effects, repeatability, accuracy and sensitivity, have to investigated to know that the machine gives reliable result when running real samples.

    Memory effects:

    Memory effect is one reason for deviation of the analysis. It is obvious that some mercury still remains within the tube after running. Memory effect is not significant at high concentration of the analyte, but could be troublesome at lower concentration.

    Repeatability:

    Repeatability was tested by running 3 replicates with the same concentration of the analyte. This is important for knowing the precision of the analysis.

    Accuracy:

    The

    Reference material MESS-92 (92ppb) was used to evaluate the accuracy of the analysis . Triplicate was running and the mean value was calculated to 98.3 ppb, the deviation was 6.86%.

    Sensitivity:

    By comparing the mercury fluorescence detector and atomic absorption (AAS) it

    become evident that the fluorescence detector is much more suitable for analysis with

    AMA 254 as it gave an overloaded signal whereas the atomic absorption only

    appeared as noise.

    Minor Field Study in Chemistry – Autumn 2010 Page 4

    The comparison between the mercury fluorescence detector and atomic absorption (AAS) was done with 0.05 gram(g) tuna fish samples. Mercury fluorescence detector gave an overloaded signal, whereas the AAS signal appeared as noise. It is evident that the fluorescence detector is much more sensitive than the AAS detector.

    Hydride generation is one common method for determining mercury in water. Three different channels are used for pumping the solutions and forming hydride, they are

    Hydrochloric acid, NaBH4and sample (blank, standards). The hydride form of mercury was flushed and collected into the gold trap by nitrogen gas. After that the gold-trap is heated up to release mercury optical cell where the absorption as a peak was measured in the same manner as normal flame AAS without using of flame.

    In our project we also made up a temperature controller to control the temperature. The real temperature was measured by thermocouple and was designed like a small box.

  • 96.
    Nordberg, Markus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Defence and Security, Systems and Technology, Norra Sorunda, Swedish Defence Research Agency (FOI), Sweden.
    Landström, Lars
    CBRN Defence and Security, Umeå, Swedish Defence Research Agency (FOI), Sweden.
    UV Raman chemical imaging using compressed sensing2019In: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 144, no 5, p. 1513-1518Article in journal (Refereed)
    Abstract [en]

    Different chemical (hyperspectral) imaging techniques have proven to be powerful tools to provide and illustrate insightful data within a broad range of research areas. The present communication includes proof-of-principle results of UV Raman hyperspectral imaging, achieved via compressed sensing measurements using coded apertures (CA) and a reconstruction algorithm. The simple and cheap CA set up, obtained by a 50% overall transmissive random binary mask (chromium on fused silica with 100 m x 100 m pixel size) positioned at the entrance plane of an imaging spectrograph, resulted in an overall high throughput for the UV region of interest. The mask was mounted on a translation stage, allowing reproducible switching to different CA, thus making possible for multi frame CA imaging. Results from a scene containing liquid droplets are shown as examples and, as expected, qualitative improvements in resolution and contrast could be observed in both the spatial and spectral domain as the number of CA frames was increased.

  • 97.
    Nordborg, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Byström, Emil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gradient polymer elution chromatography of methacrylate Telomers on monolithic capillary columns prepared by nitroxide-mediated polymerizationManuscript (preprint) (Other academic)
    Abstract [en]

    Linear methacrylate telomers prepared by isopropylxanthic disulfide photoiniferted polymerization of 2-hydroxyethyl methacrylate, methyl methacrylate, and ethyl methacrylate have been separated from their precursor monomers using gradient polymer elution chromatography (GPEC) on a monolithic capillary column. The capillary monoliths were prepared by thermally initiated radical polymerization of styrene and divinylbenzene controlled by 1-carboxy-PROXYL stable free radicals, and characterized by nitrogen adsorption and mercury intrusion porosimetry. The separations in GPEC mode were performed using a mobile phase gradient from water to methanol, where water is the non-solvent and methanol the good solvent with respect to the telomers. Successful separation of telomers from their monomer was achieved for all tested telomers. In addition, it was observed that the retention times of the intact telomers were different from those of telechelic oligomers produced by hydrolysing the isopropylxanthic terminals. The current set-up is therefore promising both for monitoring of the progress of photoiniferted polymerizations and to monitor the hydrolysis of resulting polymerized oligomers into thiol-terminated telechelics.

  • 98.
    Nordmark, Ulrika
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Quantitative determination of resin mixtures in coating colours for paper by multivariate analysis of data from pyrolysis-gas chromatography2000In: Journal of Analytical and Applied Pyrolysis, Vol. 55, no 1, p. 93-103Article in journal (Refereed)
    Abstract [en]

    Pulp and paper industries are interested in a technique for analysing the purchased resins used in coating colours. The concept of pyrolysis-gas chromatography in combination with chemometrics, i.e. principal component analysis and principal least squares, was used to develop improved methods for the quantitative analysis of tertiary mixtures based on latex resins. A principal least square model was made based on pyrolysis-gas chromatography data and a mass spectrometer was used to identify pyrolysis fragments. It was shown that the model accurately predicted the concentration of a resin in a tertiary mixture. The average error of prediction, for resin mixtures not previously shown for the model, was less than 4% by weight for each of the investigated resins.

  • 99.
    Nordmark, Ulrika
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cedergren, Anders
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Conditions for Accurate Karl Fischer Coulometry Using Diaphragm-Free Cells2000In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 72, no 1, p. 172-179Article in journal (Refereed)
    Abstract [en]

    Factors influencing the extent of formation of oxidizable reduction products in coulometric cells used for Karl Fischer (KF) determination of water were investigated. For methanolic KF reagents buffered with imidazole (Im) or diethanolamine (DEA) (separately or in combination), three parameters were found to be of outmost importance: the cathodic current density, the pH, and the concentration of protonated base (ImH+ or DEAH+). For reagents buffered with only Im, the relative formation of oxidizable reduction products varied in the range 2-40%; i.e., 51-70 g of water was found for a 50 g water sample, depending on the above-mentioned parameters. The lowest values were observed for reagents having a pH around 10 in combination with cathodic current densities in the range 2000-5000 mA cm-2. For all the Im-buffered reagents investigated, the addition of modifiers such as chloroform, hexanol, and carbon tetrachloride was found to decrease the formation of oxidizable reduction products significantly. For example, a reagent buffered at pH 10 containing 1 M hexanol gave less than 0.3% formation in the current density interval from 200 to 4000 mA cm-2. The best reagents based on the above-mentioned modifiers were tested in the continuous coulometric mode with errors typically in the interval 0-0.5% using optimum conditions. One prerequisite for obtaining such small errors with diaphragm-free continuous coulometry is to use a cathode area no larger than 0.002 cm2. For some of the reagents based on both Im and DEA, the formation of oxidizable reduction products was close to zero at certain current densities, although the analytical performance was not as good as for the reagents buffered solely by Im due to longer conditioning and titration times.

  • 100.
    Nordmark, Ulrika
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cedergren, Anders
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Progress in pulsed-current Karl Fischer coulometry using diaphragm-free cells2000In: Fresenius' Journal of Analytical Chemistry, ISSN 0937-0633, E-ISSN 1432-1130, Vol. 367, no 6, p. 519-524Article in journal (Refereed)
    Abstract [en]

    Factors influencing the accuracy of water determinations using diaphragm-free, pulsed current Karl Fischer (KF) coulometry were investigated with the new Metrohm 756 instrument. Results obtained with commercially available reagents from Riedel-deHaen and Merck were compared with home-made ones that were especially designed to minimize the formation of iodine-consuming reduction products generated in the cathode reaction. Positive errors in the range 2-5% were found for the commercial reagents as compared to 0.2-1% for the home-made ones which were buffered at about pH 10 containing modifiers like chloroform, hexanol or ethylene glycol. Except for the composition of the KF-reagent, the cathode current density and the titration rate were found to be critical parameters for the accuracy of the determinations. For all reagents investigated, the best results were obtained for the maximum generator current 400 mA (corresponding to a current density of 1400 mA cm(-2)) in combination with a maximum titration rate of 2000 mu g min(-1). Surprisingly, the errors found under optimum conditions for the pulse technique were always somewhat larger than the corresponding values obtained with continuous coulometry.

1234 51 - 100 of 186
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf