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  • 1.
    Appelblad, Patrik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry. Faculty of Medicine, Clinical Sciences.
    Ahmed, Abdu
    Umeå University, Faculty of Science and Technology, Chemistry.
    Pontén, Einar
    Umeå University, Faculty of Science and Technology, Chemistry.
    Bäckström, Torbjörn
    Faculty of Medicine, Clinical Sciences.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Perfluorosulfonated Ionomer-Modified Polyethylene. A Material for Simultaneous Solid-Phase Enrichment and Enhanced Precolumn Dansylation of C-21 Ketosteroids in Human Serum2001In: Analytical Chemistry, Vol. 73, no 15, p. 3701-8Article in journal (Refereed)
    Abstract [en]

    A new derivatization procedure has been developed where solid-phase catalysis is utilized to facilitate the formation of hydrazones in precolumn labeling of keto-containing compounds. This procedure has been implemented on a solid-phase enrichment and enhanced derivatization (SPEED) device, prepared from porous polyethylene that has been coated with Nafion and dansylhydrazine. The SPEED devices have been optimized using experimental design and characterized for dansylation of C-21 ketosteroids by multivariate data analysis, using progesterone as the model compound. The reaction temperature and the molar ratio between the steroid and the derivatization reagent were found to be the factors most strongly affecting the reaction. Faster reaction kinetics were achieved when the molar ratio between dansylhydrazine and the steroid was increased. Mass spectroscopic analysis showed that the four derivative peaks eluting when derivatized progesterone was separated on an octadecyl silica stationary phase were due to the syn and anti mono- and bis(hydrazones) formed in the reaction. Using optimal reaction conditions, the derivatives mainly constitute the syn and anti conformers of bis-derivatives. In contrast to solution-based acid catalysis, the SPEED device was remarkably insensitive to water in the reaction mixture. A sample volume of 400 L was found to be the maximum, enabling sample enrichment prior derivatization. Using optimal experimental conditions, picomole amounts of ketosteroids could be derivatized in 10 min at room temperature. Analysis of spiked serum samples containing 0.4-2.0 nmol of progesterone showed overall recoveries of 52-63%. The corresponding 3 detection limit was 1.3 pmol (n = 4, 100 L injected), as estimated from calibration curve data.

  • 2.
    Appelblad, Patrik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Separation and detection of neuroactive steroids from biological matrices2002In: Journal of Chromatography A, Vol. 955, no 2, p. 151-82Article in journal (Refereed)
    Abstract [en]

    This review is based on a selection of research papers published mainly in the last decade and it describes various analytical aspects of separation and detection of neuroactive steroids in biological matrices.

  • 3.
    Appelblad, Patrik
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Sciences. Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jonsson, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bäckström, Torbjörn
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Determination of C-21 ketosteroids in serum using trifluoromethanesulfonic acid catalyzed precolumn dansylation and 1,1’-oxalyldiimidazole postcolumn peroxyoxalate chemiluminescence detection1998In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 70, no 23, p. 5002-5009Article in journal (Refereed)
    Abstract [en]

    A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-catalyzed precolumn dansylation and coupled column liquid chromatographic separation, followed by postcolumn 1,1‘-oxalyldiimidazole peroxyoxalate chemiluminescence detection is presented. In the simultaneous optimization of chromatographic resolution and chemiluminescence intensity, a coupled column chromatographic system and a stopped-flow system were used. An eluent containing 20 mM phosphate buffer at pH 6.7 accomplished an efficient separation of 3α-hydroxy-5β-pregnan-20-one from a mixture containing 10 C-21 ketosteroids. Phosphate buffer also proved to be the most advantageous, among the six buffers tested, for sensitive detection. Experimental design and multivariate data analysis were used to characterize and optimize the postcolumn reaction chemistry in the chromatographic system. A valid full factorial design with excellent predictability showed that the flow rates for both 1,1‘-oxalyldiimidazole and hydrogen peroxide were the factors most strongly affecting the sensitivity of the system. The theoretical plate numbers were above 11 000 for all 10 dansylated ketosteroids. The 3σ detection limit estimated from 3α-hydroxy-5β-pregnan-20-one calibration curve data was 1.6 pmol (n = 4, 125 μL injected) and spiked serum containing 0−74 pmol of this compound showed overall recoveries of 73 ± 9% (n = 12). Quantitation of 3α-hydroxy-5β-pregnan-20-one was finally carried out on 45 serum samples and the results compared to those from a radioimmunoassay (RIA) method. The data acquired with the procedure described in this work compare well with the results from RIA, which confirms the reliability of the new analytical procedure.

  • 4. Appelblad, Patrik
    et al.
    Jonsson, Tobias
    Jiang, Wen
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Fast hydrophilic interaction liquid chromatographic separations on bonded zwitterionic stationary phase2008In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 31, no 9, p. 1529-1536Article in journal (Refereed)
    Abstract [en]

    Separation science is an art of obtaining adequate resolution of the desired compounds in minimum time, and with minimum effort in terms of sample preparation and data evaluation. In LC, where selectivity is a main driving force for separation, the availability of different separation modes capable of operating at high flow rates is a way to make combined optimal use of selectivity, efficiency, and speed. The separation of polar and hydrophilic compounds is problematic in RP LC due to the poor retention. Hydrophilic interaction liquid chromatography (HILIC) is a more straightforward separation mode to address this problem. Herein, it is shown that separations in HILIC mode are equally efficient as for RP, providing a potential for very fast separations on short columns. This is not only facilitated by the low viscosity of the mobile phase compositions used, compared to typical RP eluents, but also due to higher column permeability. To exemplify this, baseline separations of uracil and cytosine are shown in less than 4 s and of Tamiflu® and its main metabolite in less than 40 s, both under isocratic conditions. HILIC must therefore be considered having potential for high throughput purposes, and being an attractive candidate as the second separation dimension in 2-D HPLC.

  • 5. Basu, Basudeb
    et al.
    Paul, Susmita
    Kundu, Samir
    Byström, Emil
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Almqvist, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Organic Polymeric Resins Embedded with Pd NPs: Newly Designed, Efficient and Chemoselective Catalyst for Reduction of Nitrobenzenes2017In: Current Organocatalysis, ISSN 2213-3372, Vol. 4, no 1, p. 48-61Article in journal (Refereed)
    Abstract [en]

    Background: Organic polymer supported palladium nanoparticles (NPs) are important for use as heterogeneous catalyst in various organic reactions. This works describes Pd Nps immobilized on to polystyrene-based ion-exchange resin surface for use as catalyst in the reduction of nitrobenzenes. The heterogeneous catalyst was found useful for hydrogenation of nitro group under both catalytic transfer hydrogenation (CTH) as well as by using molecular hydrogen (H2).

    Methods: The catalyst was prepared from Amberlite IRA 900 Cl after rinsing with formic acid (10%) and subsequent treatment with Na2PdCl4 in DMF. The resulting Pd Nps immobilized resins was designated as VersaCat Pd and used for CTH of nitrobenzenes in the presence of H-donors (sodium formate, formic acid, hydrazine hydrate) and also for hydrogenation with H2 gas. The catalyst was characterized by FT-IR, MAS-NMR, SEM, TEM and XPS and surface morphologies were studied before and after the reaction.

    Results: Hydrogenations of nitrobenzenes under CTH using different H-source and direct use of H2 gas were achieved successfully with good to excellent yields. Reactions were performed under mild conditions and high degree of chemoselectivity was also observed. The catalyst was recyclable, used for six consecutive runs with appreciable conversions and showed higher activity (> 3 times) in terms of metalcontent than commercially available Pd/C (10%) in the hydrogenation of nitrobenzenes using H2 gas. The TEM images showed that Pd Nps are evenly distributed with size 50-200 mm on polymeric matrices and there was no significant changes observed after the first catalytic run. However, considerable rupture of the polymeric surface occurred after six runs, as seen from SEM studies.

    Conclusion: The present study establishes high catalytic efficiency and chemoselectivity of the newly developed organic polystyrene-based resin-soaked Pd NPs (VersaCat Pd) in the reduction of nitrobenzenes. Both CTH and hydrogenation using H2 gas were successfully done. Interestingly, hydrazine hydrate offered excellent control over chemoselectivity under CTH conditions and allowed clean conversion from nitro to amine, while keeping a chloro substitutent unaffected. Hydrogenation using molecular H2 gave maximum TOF. Easy preparation, high efficacy, TOF, chemoselectivity, and versatile applications are notable features for this heterogeneous palladium catalyst (VersaCat Pd). These features are often required in chemical industries.

  • 6.
    Bui Thi Hong, Nhat
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Verhage, Jeroen J
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tris(hydroxymethyl)aminomethane-functionalized silica particles and their application for hydrophilic interaction chromatography2010In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 33, no 19, p. 2965-2976Article in journal (Refereed)
    Abstract [en]

    A new method is presented for synthesizing a highly hydrophilic silica-based material for use in hydrophilic interaction chromatography. Porous silica particles used as a starting substrate were modified with 3-bromopropyl trichlorosilane and grafted with glycidyl methacrylate by controlled (“living”) atom transfer radical polymerization in order to introduce an oxirane-carrying reactive tentacle layer on the silica surface. The grafted material was thereafter subject to an oxirane ring opening reaction with tris(hydroxy-methyl)aminomethane in dimethylformamide to yield a polymer-bound equivalent of the well known and highly hydrophilic “TRIS” buffering substance. Chemical characterization was done by diffuse reflectance FT-IR, X-ray photoelectron spectroscopy, elemental analysis, and 1H NMR. Porosity and surface area examination was done with Brunauer–Emmett–Teller. Chromatographic application of the material was evaluated by separations of nucleic bases, small organic acids, and common nucleotides under mixed hydrophilic interaction chromatography and weak anion exchange conditions.

  • 7. Byström, Emil
    et al.
    Nordborg, Anna
    Limé, Fredrik
    Dinh, Ngoc Phuoc
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Plasma brominated polymer particles as grafting substrate for thiol-terminated telomers2010In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 33, no 11, p. 1563-70Article in journal (Refereed)
    Abstract [en]

    A combined surface activation and "grafting to" strategy was developed to convert divinylbenzene particles into weak cation exchangers suitable for protein separation. The initial activation step was based on plasma modification with bromoform, which rendered the particles amenable to further reaction with nucleophiles by introducing Br to a surface content of 11.2 atom-%, as determined by X-ray photoelectron spectroscopy. Grafting of thiol-terminated glydicyl methacrylate telomers to freshly plasma activated surfaces was accomplished without the use of added initiator, and the grafting was verified both by reduction in bromine content and the appearance of sulfur-carbon linkages, showing that the surface grafts were covalently bonded. Following grafting the attached glydicyl methacrylate telomer tentacles were further modified by a two-step procedure involving hydrolysis to 2,3-hydroxypropyl groups and conversion of hydroxyl groups to carboxylate functionality by succinic anhydride. The final material was capable of baseline separating four model proteins in 3 min by gradient cation exchange chromatography in a fully aqueous eluent.

  • 8.
    Byström, Emil
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Viklund, Camilla
    Merck SeQuant AB, Umeå.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Differences in porous characteristics of styrenic monoliths prepared by controlled thermal polymerization in molds of varying dimensions2010In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 33, no 2, p. 191-199Article in journal (Refereed)
    Abstract [en]

    Nitroxide-mediated polymerization was used as a model system for preparing styrenic monolithic materials with significant mesopore contents in different mold formats, with the aim of assessing the validity of pore characterization of capillary monoliths by analysis of parallel bulk polymerized precursor solution. Capillary monoliths were prepared in 250 mm id fused silica tubes (quadruplicate samples, in total 17 m), and the batch polymerizations were carried out in parallel in 100 mL microvials and regular 2mL glass vials, both in quintuplicate. The monoliths recovered from the molds were characterized for their meso- and macroporous properties by nitrogen sorptiometry (three repeated runs on each sample), followed by a single analysis by mercury intrusion porosimetry. A total of 14 monolith samples were thus analyzed. A Grubbs’ test identified one regular vial sample as an outlier in the sorptiometric surface area measurements, and data from this sample were consequently excluded from the pore size calculations, which are based on the same nitrogen sorption data, and also from the mercury intrusion data set. The remaining data were subjected to single factor analyses of variance analyses to test if the porous properties of the capillary monoliths were different from those of the bulk monoliths prepared in parallel. Significant differences were found between all three formats both in their meso and macroporous properties. When the dimension was shrunk from conventional vial to capillary size, the specific surface area decreased from 52.274.7 to 34.671.7m2/g. This decrease in specific surface area was accompanied by a significant shift in median diameter of the through-pores, from 31073.9 to 544713 nm. None of these differences was obvious from the scanning electron micrographs that were acquired for each sample type. The common practice of determining the mesopore characteristics from analysis of samples prepared by parallel bulk polymerization and looking for changes in the macropore structure by visual assessment of SEMs are therefore both rather questionable, at least for monoliths of the kind used in this study.

  • 9.
    Courtois, Julien
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Fischer, Gerd
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sellergren, Börje
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Molecularly imprinted polymers grafted to flow through poly(trimethylolpropane trimethacrylate) monoliths for capillary-based solid-phase extraction2006In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1109, no 1, p. 92-99Article in journal (Refereed)
    Abstract [en]

    Monolithic previous termmolecularly imprinted polymersnext term (mMIPs) have been synthesized in a novel way using a trimethylolpropane trimethacrylate core material photo-polymerized in situ in a 100 μm I.D. UV-transparent capillary and further photo-previous termgraftednext term to create specific cavities in the previous termgraftednext term layer. This polymerization technique allows the imprints to be directly created on the surface of the material using a minimum amount of template. Three different anaesthetics of similar structures (bupivacaine, mepivacaine and S-ropivacaine) were used as model target molecules to synthesize sample enrichment media. Hence, various mMIPs have been prepared and evaluated on a micro-system against each analyte in order to test the retention properties and cross-selectivities of the materials. The retention factors were determined and compared with the non-previous termimprintednext term reference column (mNIP), yielding high imprinting factors together with good selectivity factors between the three analytes. A study with a pure enantiomeric target was carried out to assess the degree of stereo-specific imprinting for injection of racemic mixtures. Finally, one column was previous termimprintednext term with an equimolar mixture of all three anaesthetics to provide further comprehension of the retention mechanism and accredit the possibility of using the material as a sample enrichment entity. Scanning electron microscopy (SEM), nitrogen absorption/desorption (BET) and mercury intrusion porosimetry were used to characterize the monolith and the mMIPs properties. Nuclear magnetic resonance (NMR) has been used to assess the similarities between the mMIP and mNIP.

  • 10.
    Courtois, Julien
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Szumski, M
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Byström, Emil
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Iwasiewicz, Agnieszka
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries.2006In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 29, no 1, p. 14-24Article in journal (Refereed)
    Abstract [en]

    Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent.

  • 11.
    Courtois, Julien
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Szumski, Michal
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Georgsson, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Assessing the macroporous structure of monolithic columns by transmission electron microscopy2007In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 79, no 1, p. 335-344Article in journal (Refereed)
    Abstract [en]

    A set of monolithic stationary phases representing a broad span of monomers and porogens have been characterized directly in their capillary chromatographic format by computational assessment of their pore structure from transmission electron micrographs obtained after in situ embedment of the monoliths in contrast resin, followed by dissolution of the fused-silica tubing, further encasement of the resin-embedded monolith, and microtomy. This technique has been compared to mercury intrusion, a more conventional technique for macroporosity estimation. Supplementing the embedding resin by lead methacrylate gave a negative staining, and the resulting micrographs showed a good contrast between the polymeric monoliths and the embedding resin that allowed studies on the pore formation and polymer development. The technique was also applied to a commercial monolithic silica column.

  • 12.
    Dinh, Ngoc Phuoc
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jonsson, Tobias
    Merck SeQuant AB, S-90719 Umeå, Sweden.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Accumlations of ammonium acetate on polar materials under HILIC condition and its relation to retention of analytesManuscript (preprint) (Other academic)
    Abstract [en]

    Ammonium acetate is a buffer salt commonly added to mobile phase in HILIC to improve the reproducibility of the retention of analytes. Adding buffer salt would then result to the change in retention and selectivity. In this study, we have developed methods for determine ammonium acetate in form of its hydrolyzed products (ammonium ion and acetate ion) adsorption on twelve different HILIC stationary phases under various mobile phase condition. The effect of functional group and mobile phase compositions on salt adsorption was then discussed. We also tried to develop a method for characterization important retention mechanism of HILIC systems and interpreted them under the relationship with salt adsorption. Adsorption of salt was based on both portioning and electrostatic interaction. Ammonium was found to preferentially adsorb on HILIC stationary phases except Purospher Star NH2 phase. It is worth noting that adding salt to mobile phase can promote partitioning retention mechanism, possibly as a result of phase separation due to salt out effect.

  • 13.
    Dinh, Ngoc Phuoc
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jonsson, Tobias
    Merck SeQuant AB, Box 7956, S-90719 Umeå, Sweden.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Probing the interaction mode in hydrophilic interaction chromatography2011In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 35, p. 5880-5891Article in journal (Refereed)
    Abstract [en]

    This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. "Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole, π-π interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar.

  • 14.
    Dinh, Ngoc Phuoc
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Merck SeQuant AB, Umeå.
    Jonsson, Tobias
    Merck SeQuant AB, Umeå.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention2013In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1320, p. 33-47Article in journal (Other academic)
    Abstract [en]

    In hydrophilic interaction chromatography, water is known to accumulate on the stationary phase to form a water enriched layer, which is believed to play an important role in the retention mechanism. To gain a better understanding retention mechanism in HILIC, we have determined the water uptake on twelve different HILIC stationary phases. Non-modified and monomerically functionalized silica phases followed a pattern of monolayer formation followed by multiple layer adsorption, while the water uptake on polymerically functionalized silica stationary phase showed the characteristics of formation and swelling of hydrogels. This difference in the nature of water accumulation was found to be related to different water uptake patterns when methanol and tetrahydrofuran were added to 80:20 % (v/v) acetonitrile/water by replacing 5 % of the acetonitrile as tertiary solvents, and also when ammonium acetate was added as buffering electrolyte. The relationship between water uptake and retention mechanism was investigated by looking at the correlation between retention factors of neutral analytes and phase ratios of HILIC columns, calculated either as surface area (adsorption) or volume of the water layer enriched from the acetonitrile/water eluent (partitioning). Regardless of the adsorption or partitioning mechanism, the interaction of neutral analytes and stationary phase could be mainly the hydrogen bonding between analytes and the accumulated water in the water enriched layer.

  • 15.
    Dinh, Ngoc Phuoc
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nguyen, Anh Mai
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Quach, Minh Cam
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrei
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Functionalization of epoxy-based monoliths for ion exchange chromatography of proteins2009In: Journal of Separation Science, Vol. 32, no 15-16, p. 2556-2564Article in journal (Refereed)
    Abstract [en]

    Macroporous epoxy-based monoliths prepared by emulsion polymerization have been modified for use in ion exchange chromatography (IEC) of proteins. Strong anion exchange functionality was established by iodomethane quaternization of tertiary amine present on the monolith surface as a part of the polymer backbone. The modification pathway to cation exchange materials was via incorporation of glycidyl methacrylate (GMA) brushes which were coated using atom transfer radical polymerization (ATRP). Strong (SO3-) and weak (COO-) cation exchange groups were thereafter introduced onto the GMA-grafted monoliths by reactions with sodium hydrogen sulfite and iminodiacetic acid, respectively. Grafting was confirmed by XPS, gravimetric measurement, and chromatographic behavior of the modified materials toward model proteins. In incubation experiments the proteins were recovered quantitatively with no obvious signs of unfolding after contact with the stationary phase for >2 h. Chromatographic assessments on the functionalized columns as well as problems associated with flow-through modification by ATRP are discussed.

  • 16.
    Elhaj, Ahmed
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Baytekin, Mehmet
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Porous Melamine-Formaldehyde Monoliths by Step-Growth Polymerization Reactions via an Organic Sol-gel ProcessIn: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093Article in journal (Refereed)
    Abstract [en]

    In this explorative study, twenty hydrophilic melamine-formaldehyde (MF) monolith materials were syn­the­sized by acid-catalyzed polycon­densation of systems consisting of an aqueous MF pre­condensate, a block copolymeric surfactant as main porogen, and short aliphatic polyethers as co-porogens, which were dispersed in three different organic solvents covering a wide span in polarity. The molecular size and type of aliphatic polyether (co-porogen), and of the ratio of solvents to the other components were investigated by an experimental design that resulted in monolithic materials covering a wide range of different meso- and macroporous properties. A multivariate assessment revealed that the strongest contributors to the mesopore size and the inversely related surface area were the co-porogens, whereas the macropore dimension was explained by the solvents and the ratio between solvents and the other components. Surface elemental analysis by XPS showed slight differen­ces in the bridging type between monoliths of opaque glass-like vs. white solid appearance. Measurements ζ-potentials in 10 mM ammonium acetate showed that the MF monoliths had no net charge at neutral pH, and +11 and –13 mV at pH 4 and 9.5, respectively.

  • 17.
    Elhaj, Ahmed
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Monolithic space-filling porous materials from engineering plastics by thermally induced phase separation2014In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 6, no 18, p. 15653-15666Article in journal (Refereed)
    Abstract [en]

    Six different uncompounded engineering and commodity polymers were evaluated for their ability to produce space-filling monolithic entities by thermally induced phase separation (TIPS) from 22 different solvents. Attempts were first made to dissolve the polymers at elevated temperatures, selected below the boiling point of each solvent. Then the solutions of polymers that were homogeneous dissolved underwent a controlled temperature decrease to induce a phase separation as the upper critical solution temperature was passed. Twelve of the solvents gave monolithic entities by this procedure, materials that were characterized with regard to their specific surface area and pore size distribution. These measured parameters were then correlated with their macroporous morphology, assessed by scanning electron microscopy. Monolithic materials with widely different mesoporous properties were obtained with specific surface areas ranging from 169 m(2)/g to structures with essentially nonporous skeletons and distinct mesopore size distribution modes from 6 to 15 nm. The materials furthermore had a wide variation in their macroporous morphologies-among the same polymer processed in different solvents and between different polymers dissolved in the same solvent. TIPS processing therefore appears to be a viable route to prepare space-filling meso- and macroporous support materials for a wide variety of purposes in separation science and heterogeneous chemistry.

  • 18.
    Elhaj, Ahmed
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Porous Space-filling Monolithic Polyvinylidene Difluoride (PVDF) Materials by Thermally Induced Phase SeparationIn: Polymer, ISSN 0032-3861, E-ISSN 1873-2291Article in journal (Refereed)
    Abstract [en]

    Thermally induced phase separation was assessed as a means of producing space-filling monoliths from PVDF of three dif­ferent molecular weights in twenty-two different solvents spanning a wide polarity range. Monolithic materials were produced in six out of these solvents; n-butyl butyrate, 1,4-dimethoxy­benzene, cyclohexanone, 2,5-hexanedione, dimethyl succinate, and e-caprolact­one. These monoliths had specific surface areas up to 35 m2/g, with the majority of the measured sur­face area attributable to pores in the mesoporous region from 5-20 nm, depending on solvent. Scanning elec­tron microscopy images re­vealed radically different structures at the macropore level. In three of the samples essentially monodis­perse particles in the 4-5 µm diameter range were found and verified to be of the same chemical compo­sition as the monolithic part of the precipitate. These particles appeared for PVDF of different mole­cular weights and seem to have phase separated by a mechanism dif­fering from the bulk monolith, which could hint at a novel way to prepare monodisperse PVDF particles.

  • 19. Emgenbroich, Marco
    et al.
    Borrelli, Cristiana
    Shinde, Sudhirkumar
    Lazraq, Issam
    Vilela, Filipe
    Hall, Andrew J
    Oxelbark, Joakim
    De Lorenzi, Ersilia
    Courtois, Julien
    Simanova, Anna
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Verhage, Jeroen
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Karim, Kal
    Sellergren, Börje
    A Phosphotyrosine-Imprinted Polymer Receptor for the Recognition of Tyrosine Phosphorylated Peptides2008In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 14, no 31, p. 9516-29Article in journal (Refereed)
    Abstract [en]

    Hyperphosphorylation at tyrosine is commonly observed in tumor proteomes and, hence, specific phosphoproteins or phosphopeptides could serve as markers useful for cancer diagnostics and therapeutics. The analysis of such targets is, however, a challenging task, because of their commonly low abundance and the lack of robust and effective preconcentration techniques. As a robust alternative to the commonly used immunoaffinity techniques that rely on phosphotyrosine(pTyr)-specific antibodies, we have developed an epitope-imprinting strategy that leads to a synthetic pTyr-selective imprinted polymer receptor. The binding site incorporates two monourea ligands placed by preorganization around a pTyr dianion template. The tight binding site displayed good binding affinities for the pTyr template, in the range of that observed for corresponding antibodies, and a clear preference for pTyr over phosphoserine (pSer). In further analogy to the antibodies, the imprinted polymer was capable of capturing short tyrosine phosphorylated peptides in the presence of an excess of their non-phosphorylated counterparts or peptides phosphorylated at serine.

  • 20.
    Hemström, Petrus
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Hydrophilic interaction chromatography2006In: Journal of Separation Science, Vol. 29, p. 1784-1821Article in journal (Refereed)
    Abstract [en]

    Separation of polar compounds on polar stationary phases with partly aqueous eluents is by no means a new separation mode in LC. The first HPLC applications were published more than 30 years ago, and were for a long time mostly confined to carbohydrate analysis. In the early 1990s new phases started to emerge, and the practice was given a name, hydrophilic interaction chromatography (HILIC). Although the use of this separation mode has been relatively limited, we have seen a sudden increase in popularity over the last few years, promoted by the need to analyze polar compounds in increasingly complex mixtures. Another reason for the increase in popularity is the widespread use of MS coupled to LC. The partly aqueous eluents high in ACN with a limited need of adding salt is almost ideal for ESI. The applications now encompass most categories of polar compounds, charged as well as uncharged, although HILIC is particularly well suited for solutes lacking charge where coulombic interactions cannot be used to mediate retention. The review attempts to summarize the ongoing discussion on the separation mechanism and gives an overview of the stationary phases used and the applications addressed with this separation mode in LC.

  • 21.
    Hemström, Petrus
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nordborg, Anna
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Svec, Frantisek
    Fréchet, Jean M. J.
    Polymer-based monolithic microcolumns for hydrophobic interaction chromatography of proteins.2006In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 29, no 1, p. 25-32Article in journal (Refereed)
    Abstract [en]

    Monolithic capillary columns for hydrophobic interaction chromatography (HIC) have been prepared by thermally initiated, single-step in situ polymerization of mixtures of monovinyl monomers including butyl methacrylate and/or 2-hydroxyethyl methacrylate, with a divinyl crosslinker glycerol dimethacrylate or 1,4-butanediol dimethacrylate using two different porogen systems. Two porogenic solvent mixtures were used; one "hydrophilic", consisting of water, butanediol, and propanol, and one "hydrophobic," comprising dodecanol and cyclohexanol. The porous structures of the monoliths were characterized and their performance was demonstrated with a separation of a mixture of myoglobin, ribonuclease A, and lysozyme under conditions typical of HIC.

  • 22.
    Hemström, Petrus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nygren, Yvonne
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Björn, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Alternative organic solvents for HILIC separation of cisplatin species with on-line ICP-MS detection2008In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 31, no 4, p. 599-603Article in journal (Refereed)
    Abstract [en]

    Several low volatile organic solvents were evaluated as organic modifiers in eluents for HILIC separations of cisplatin species to optimize the on-line coupling of HILIC to inductively coupled plasma MS (ICP-MS). The aim was to identify a solvent giving low solvent vapor loading of the ICP, to maximize analyte sensitivity and minimize carbon depositions on instrumental parts, while retaining chromatographic performance. The best overall performance of the HILIC-ICP-MS system for the analysis of cisplatin was achieved using 1,4-dioxane as eluent, yielding high retention and an HILIC type retention mechanism, at the expense of a 50% drop in column efficiency due to the higher viscosity of 1,4-dioxane compared to the more commonly used HILIC solvent ACN. Using 1,4-dioxane as solvent in HILIC provides the best compromise between carbon deposition and separation efficiency among a series of high-boiling water-miscible solvents tested.

  • 23.
    Hemström, Petrus
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Szumski, Michal
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Atom-transfer radical graft polymerization initiated directly from silica applied to functionalization of stationary phases for high-performance liquid chromatography in the hydrophilic interaction chromatography mode.2006In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 78, no 20, p. 7098-7103Article in journal (Refereed)
    Abstract [en]

    Initiation of atom-transfer radical polymerization of a number of monomers (styrene, methyl acrylate, 3-[N,N-dimethyl-N-(methacryloyloxyethyl)ammonium] propanesulfonate, butyl methacrylate, 2,3-epoxypropyl methacrylate) directly from chlorinated porous silica particles has been performed. The grafting has been confirmed and evaluated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. This initiation technique results in a hydrolytically stable initial Si-C bond, tethering the polymer to the silica substrate. The resulting grafted particles have been used as separation materials for both reversed-phase and hydrophilic interaction chromatography.

  • 24.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    High-Performance Liquid Chromatography of Biological Macromolecules2000In: Encyclopedia of Analytical Chemistry, John Wiley & Sons, Ltd., Chichester , 2000, p. 403-528Chapter in book (Other academic)
    Abstract [en]

    This article has no abstract.

  • 25.
    Jiang, Wen
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Fischer, Gerd
    Umeå University, Faculty of Science and Technology, Chemistry.
    Girmay, Yohannes
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Zwitterionic stationary phase with covalently bonded phosphorylcholine type polymer grafts and its applicability to separation of peptides in the hydrophilic interaction liquid chromatography mode2006In: Journal of Chromatography A, Vol. 1127, p. 82-91Article in journal (Refereed)
    Abstract [en]

    A novel phosphorylcholine type zwitterionic stationary phase was synthesized by graft polymerization of 2-methacryloyloxyethyl phosphorylcholine onto the surface of porous silica particles. The resulting material possesses both negatively charged phosphoric acid and positively charged quaternary ammonium groups, which renders it a low net charge over a wide pH range. The composition of the surface grafts were determined by elemental analysis and solid state NMR, and the surface charge (zeta-potential) in different buffer solutions were measured using photon correlation spectroscopy. Separation of several peptides was investigated on packed columns in the hydrophilic interaction liquid chromatography (HILIC) separation mode. It was shown that small peptides can be separated based on hydrophilic interaction and ionic interaction between the stationary phase and analyte. The organic solvent composition, the pH and the salt concentration of the eluent have strong effects on the retention time. Compared to native silica before grafting, the newly synthesized zwitterionic material gave more stable retention times for basic peptides over pH range 3–7 due to elimination of the dissociation of silanol groups.

  • 26.
    Jiang, Wen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Characterization of polymeric zwitterionic stationary phase and application for protein separationManuscript (preprint) (Other academic)
  • 27.
    Jiang, Wen
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Synthesis and Evaluation of Polymer-Based Zwitterionic Stationary Phases for Separation of Ionic Species2001In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 73, no 9, p. 1993-2003Article in journal (Refereed)
    Abstract [en]

    Three different zwitterionic functional stationary phases for chromatography were synthesized on the basis of 2-hydroxyethyl methacrylate (HEMA) polymeric particles. Two synthesis routes, producing materials designated S300-ECH-DMA-PS or S300-TC-DMA-PS, involved activation of the hydroxyl groups of the HEMA material with epichlorohydrin or thionyl chloride, respectively, followed by dimethylamination and quaternizing 3-sulfopropylation with 1,3-propane sultone. The third route was accomplished by attaching methacrylate moieties to the HEMA through a reaction with methacrylic anhydride, followed by graft photopolymerization of the zwitterionic monomer 3-[N,N-dimethyl-N-(methacryloyloxyethyl)ammonium] propanesulfonate, initiated by benzoin methyl ether under 365-nm light. According to elemental analyses, both the S300-ECH-DMA-PS and S300-TC-DMA-PS materials appeared to have overall charge stoichometries close to unity, whereas the grafted material, S300-MAA-SPE, seemed to carry an excess of anion exchange sites in addition to the zwitterionic groups. Yet all three zwitterionic stationary phases were capable of separating inorganic anions and cations simultaneously and independently using aqueous solutions of perchloric acid or perchlorate salts as eluent, albeit with markedly different selectivities. On the S300-TC-DMA-PS and S300-MAA-SPE materials, the retention times increased for cations and decreased for anions with increasing eluent concentration, whereas with the S300-ECH-DMA-PS material, the retention times of both anions and cations decreased with increasing eluent concentration. These results demonstrate the importance of choosing appropriate synthesis conditions in order to prepare covalently bonded zwitterionic separation materials with an acceptable charge balance.

  • 28.
    Jiang, Wen
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Tentacle-Type Zwitterionic Stationary Phase Prepared by Surface-Initiated Graft Polymerization of 3-[N,N-Dimethyl-N-(Methacryloyloxyethyl)- ammonium] Propanesulfonate through Peroxide Groups Tethered on Porous Silica2002In: Analytical Chemistry, Vol. 74, no 18, p. 4682-7Article in journal (Refereed)
    Abstract [en]

    A novel stationary phase with tentacle-type zwitterionic interaction layer was synthesized by free radical graft polymerization of 3-[N,N-dimethyl-N-(methacryloyloxyethyl)ammonium]propanesulfonate (SPE) from the surface of Kromasil porous silica particles. The polymerization was initiated by thermal cleavage of tert-butylperoxy groups covalently attached to the particle surface, and the material therefore carries a tentacle-type polymeric interaction layer with 3-sulfopropylbetaine functional moieties. The composition of the surface graft was determined by elemental analysis, and the surface charge was measured using photon correlation spectroscopy. The measured -potentials were close to 0 and nearly independent of pH, and the tentacle character of the interactive layers were evident from the lack of colloidal stability in the absence of salt (antipolyelectrolytic behavior) and a marked increase in column back-pressure when the concentration of perchloric acid or perchlorate salt was increased. The chromatographic properties were evaluated on columns packed with the functionalized material, and it was shown that this zwitterionic stationary phase could simultaneously and independently separate inorganic anions and cations using aqueous solutions of perchloric acid or perchlorate salts as eluents. The material was also capable of separating two acidic and three basic proteins in a single run, using gradient salt elution at constant pH.

  • 29.
    Jonsson, T
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    New nucleophilic catalysts for bright and fast peroxyoxalate chemiluminescence2000In: ANALYTICAL CHEMISTRY, Vol. 72, no 7, p. 1373-80Article in journal (Refereed)
    Abstract [en]

    Miniaturized detection applications based on chemiluminescence require fast reaction kinetics for optimum performance. in this work, high-intensity light from the analytically useful peroxyoxalate chemiluminescence reaction has been generated at high rates by employing both single-component and dual-component nucleophilic catalysis. 4-(Dimethylamino)pyridine and its derivatives were superior to all other bases in terms of reaction speed and intensity of the generated light and outshone imidazole, which hitherto has been considered as the best catalyst, The light intensity was related to the difference in pK(a) between the 4-aminopyridine catalyst and the leaving group of the reagent, and the optimum Delta pK(a) was found to be close to 0. Similarly, high light intensities were obtained when mixtures of the imidazole analogue 1,2,4-triazole and the strong, nonnucleophilic base 1,2,2,6,6-pentamethylpiperidine acted as catalysts, The mechanism behind this was concluded to be a "base-induced nucleophilic catalysis", where the ancillary strong base assisted the production of the highly nucleophilic 1,2,4-triazolate anion, which as the actual catalyst then participated in the formation of a more reactive transient reagent. All the investigated catalysts reduced the light yield of the reaction due to base-catalyzed breakdown reactions of the reagents and/or intermediates. The intensity peak maximums of these bright and fast reactions typically appeared after less than 10 ms, whereafter the light decayed to darkness within a few seconds, These reaction characteristics are especially advantageous for sensitive detection applications where the observation volumes and times are limited, e.g., peaks emerging from a capillary-based separation process.

  • 30.
    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.

  • 31.
    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.

  • 32.
    Limé, Fredrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hydrobromination of residual vinyl groups on divinylbenzene polymer particles followed by atom transfer radical surface graft polymerization2009In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 47, no 5, p. 1259-1265Article in journal (Refereed)
    Abstract [en]

    Rigid and monodisperse spherical polymer particles with 2.36 ± 0.18 m diameter containing residual surface vinyl groups were prepared by photoinitiated precipitation polymerization of divinylbenzene. Anti-Markovnikov addition of HBr to the surface vinyl groups yielded a 2-bromoethyl functionality that was used as macroinitiator for atom transfer radical polymerization (ATRP), providing the possibility for further functionalization by controlled grafting from processes. This was demonstrated by grafting of glycidyl methacrylate brushes from the particle surface, using an ATRP system based on CuBr and pentamethyl diethylenetriamine. Existence of a methacrylic overlayer was verified by FTIR and XPS measurements, and the grafted particles were easily dispersed in water, confirming conversion of the particle surface from hydrophobic to hydrophilic. Hydrobromination of residual vinyl groups yields a macroinitiator that can be used for grafting of glycidyl methacrylate by ATRP.

  • 33.
    Limé, Fredrik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Monodisperse Polymeric Particles by Photoinitiated Precipitation Polymerization2007In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Macromolecules, Vol. 40, no 6, p. 1962-1968Article in journal (Refereed)
    Abstract [en]

    Monodisperse polymer particles consisting of DVB and styrene-copoly-DVB were successfully synthesized by photoinitiated precipitation polymerization with 2,2'-azobis(2-methylpropionitrile) (AIBN) as initiator. A focused 150 W xenon short arc lamp was used to radiate the sample mixtures. The size of the particles ranged from 1.5 to 4 m and could be varied by changing the monomer concentration between 2 and 10% (v/v) and by means of the time of polymerization. By using photoinitiation instead of thermal initiation, it was possible to avoid coagulum and arrive at spherical particles with an exceptionally high monodispersity for particles of this size range (polydispersity index < 1.02) and with monomer loadings well above 5%.

  • 34.
    Limé, Fredrik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Polymerization of Divinylbenzene and Divinylbenzene-co-Glycidyl Methacrylate Particles by Photoinitiated Precipitation Polymerization in Different Solvent MixturesManuscript (preprint) (Other (popular science, discussion, etc.))
  • 35.
    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.

  • 36.
    Liu, Mingquan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tran, Tri Minh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Elhaj, Ahmed Awad Abbas
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Torsetnes, Silje Boen
    Jensen, Ole N.
    Sellergren, Borje
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Molecularly Imprinted Porous Monolithic Materials from Melamine-Formaldehyde for Selective Trapping of Phosphopeptides2017In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 89, no 17, p. 9491-9501Article in journal (Refereed)
    Abstract [en]

    Thirty-five melamine formaldehyde (MF) monolithic materials with bimodal pore distributions were synthesized in fused silica capillaries by catalyst-free polycondensation, starting with an aqueous MF precondensate, using acetonitrile as the macroporogen and a variety of aliphatic polyethers and triblock copolymeric surfactants as porogens and mesoporogens, respectively. By varying the prepolymer composition and the type and molecular weight of the polymeric porogen components, a library of porous monolithic materials was produced, covering a range of meso- and macroporous properties. A multivariate evaluation revealed that the amount of surfactant was the strongest contributor to specific surface area and pore volume and to the inversely related mesopore size, whereas the macropore dimensions were controlled mainly by the amount of aliphatic polyether porogen. One of these capillary monoliths, chosen based on the combination of meso- and macropores providing optimal percolative flow and accessible surface area, was synthesized in the presence of N-Fmoc and O-Et protected phosphoserine and phosphotyrosine to prepare molecularly imprinted monoliths with surface layers selective for phosphopeptides. These imprinted monoliths were characterized alongside nonimprinted monoliths by a variety of techniques and finally evaluated by liquid chromatography mass spectrometry in the capillary format to assess their abilities to trap and release phosphorylated amino acids and peptides from partly aqueous media. Selective enrichment of phosphorylated targets was demonstrated, suggesting that these materials could be useful as trapping media in-affinity-based phosphoproteomics.

  • 37.
    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.

  • 38.
    Nguyen, Anh Mai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Dinh, Ngoc Phuoc
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cam, Quach Minh
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sparrman, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Preparation and characterization of sizable macroporous epoxy resin-based monolithic supports for flow-through systems2009In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 32, no 15-16, p. 2608-2618Article in journal (Refereed)
    Abstract [en]

    This paper presents further results from our efforts to prepare sizable macroporous monolithic materials from epoxy resins and polyamines by emulsion polymerization. For their uses as supports in flow systems, the study aimed at developing materials possessing maximum fluid permeability, high mechanical stability, and a controlled porosity and surface area. Characterization of the materials has been carried out using different techniques, focusing on morphological and mechanical features, and on the surface chemistry. Morphology and porosity were studied with SEM, nitrogen adsorption/desorption, mercury intrusion porosimetry (MIP), and (2)H NMR cryoporosimetry. The chemical composition of the bulk structures and their surfaces was studied by means of bulk elemental analysis and X-ray photoelectron spectroscopy, and potentiometric titration was used to assess the relative amounts of amines and epoxy groups. Essentially, the morphological features were a high fluid permeability, but rather low specific surface area. Convective flow was facilitated by large, interconnected, and evenly spaced macropores which were formed by nonporous skeletons of the connected-rod type. Despite the interfacial nature of the polymerization, the bulk and the surface of the fully cured materials showed similar elemental compositions. All materials were found to have a high surface density of hydroxyl groups, which facilitates functionalization reactions.

  • 39.
    Nguyen, Anh Mai
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Epoxy-Based Monoliths. A Novel Hydrophilic Separation Material for Liquid Chromatography of Biomolecules2006In: Chemistry of Materials, Vol. 18, no 26, p. 6308-15Article in journal (Refereed)
    Abstract [en]

    In our efforts to develop novel hydrophilic monolithic porous materials for use as supports in liquid chromatographic separation of proteins, polymers based on epoxy monomers and diamines as curing agents were synthesized. The epoxy dispersed phase was emulsified in an aqueous phase containing the amine with the aid of a nonionic polymeric surfactant, and the resulting emulsions were thermally polymerized. Various factors, namely, the type of epoxy component, levels of reactants, type and concentration of diluents, and curing procedures, were studied to obtain suitable morphology and adequate mechanical properties for their intended use. Characterization of their morphologies and porous properties was done using scanning electron microscopy, nitrogen adsorption/desorption measurement (BET method), mercury intrusion porosimetry, and X-ray photoelectron spectroscopy.

  • 40.
    Nguyen, Anh Mai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nguyen, Thanh Duc
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sizeable Macroporous Monolithic Polyamide Entities Prepared in Closed Molds by Thermally Mediated Dissolution and Phase Segregation2008In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 20, no 19, p. 6244-6247Article in journal (Refereed)
    Abstract [en]

    A simple method is presented for the preparation of macroporous monoliths from an aliphatic polyamide in closed molds, based on swelling/dissolution in benzyl alcohol at elevated temperature, followed by precipitation into a continuous monolithic structure by cooling the solution below the upper critical solution temperature. Subsequent removal of the solvent led to the formation of rigid macroporous nylon monoliths with a continuous and evenly spaced macropore system. The intended use is as supports for flow-through systems, where efficient mass transport at low flow resistance is the key optimization criterion.

  • 41.
    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.

  • 42.
    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.

  • 43.
    Nordborg, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    A Library of Thiol-Terminated Methacrylate Telomers Prepared by Photoinitiated Iniferter Mediated Polymerization for Use in Modifications of Chromatographic Surfaces by the "Grafting to" Approach2010In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 117, no 5, p. 2781-2789Article in journal (Refereed)
    Abstract [en]

    A library of thiol-terminated methacrylate telomers aimed for use in surface modifications of chromatographic support materials has been prepared by iniferter mediated polymerization, using isopropylxanthic disulfide as a photoiniferter. The telomers range from hydrophobic to hydrophilic and were prepared in different lengths, with the length being adjusted by the ratio of monomer to iniferter used in the polymerization mixture. The telomers were characterized by size-exclusion chromatography and MALDI-TOF-MS. In initial surface characterization experiments, the prepared telomers were attached to the inner surface of fused silica capillaries by radical initiated addition to vinyl groups, and the electro-osmotic flow (