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Noise characteristics and analytical precision of inductively coupled plasma mass spectrometry using a Vulkan direct injection nebuliser for sample introduction
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Clinical chemistry.
2006 (English)In: Journal of Analytical Atomic Spectrometry, ISSN 0267-9477, E-ISSN 1364-5544, Vol. 22, no 2, 168-176 p.Article in journal (Refereed) Published
Abstract [en]

Noise and precision of ion count rate measurements were characterised for ICP-MS using a Vulkan direct injection nebuliser (Vulkan DIN) for sample introduction. For comparison, experiments were also carried out using a direct injection high efficiency nebuliser (DIHEN). The Vulkan DIN gave considerably higher relative white noise compared with the DIHEN, −40.3 compared with −45.8 dB, and measurements of aerosol characteristics showed that this was a result of broader size distribution and larger mean size of droplets for the Vulkan DIN. At a liquid flow rate of 85 μL min−1, the aerosol volume fraction constituted by droplets with a diameter smaller than 10 μm was only 5% for the Vulkan DIN compared to 38% for the DIHEN, and the Sauter mean diameter was 30.2 and 11.1 μm, respectively. Compared with the DIHEN, interference noise from a peristaltic pump was very small with the Vulkan DIN because at the liquid flow rate giving maximum sensitivity, the analyte signal intensity was not much affected by changes in liquid flow rate. Although this had a positive effect on precision, it indicated that the plasma is cooled by large droplets that do not positively contribute to the analyte signal intensity. For analytical precision data it was evident that with the Vulkan DIN, precision was limited by the high white noise in the frequency range 0.4–500 Hz, but for the DIHEN there were relatively large contributions from 1/f and/or interference noise to the observed precision. When using integration times of 1000 ms or longer, the DIHEN did, however, appear to give slightly better precision for most of the isotopes tested. For comparison, precision data was also generated when using a conventional spray chamber sample introduction system and it was found that, with a 3000 ms integration time, both direct injection nebulisers gave better precision for most isotopes. Although analytical precision is impressive, the results in this paper also show that both direct injection nebulisers produce aerosols that are far from ideal for the types of ICPs currently used in commercial instruments.

Place, publisher, year, edition, pages
London: Royal Society of Chemistry , 2006. Vol. 22, no 2, 168-176 p.
URN: urn:nbn:se:umu:diva-4914DOI: 10.1039/b514503aOAI: diva2:144194
Available from: 2006-01-12 Created: 2006-01-12 Last updated: 2011-04-05Bibliographically approved
In thesis
1. Fundamental Studies on Direct Injection Nebulisers for Sample Introduction in ICP Spectrometry: Aerosol Properties, ICP Characteristics and Analytical Performance
Open this publication in new window or tab >>Fundamental Studies on Direct Injection Nebulisers for Sample Introduction in ICP Spectrometry: Aerosol Properties, ICP Characteristics and Analytical Performance
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The performance of different types of nebulisers: Vulkan direct injection nebuliser (Vulkan DIN), direct injection high efficiency nebuliser (DIHEN), microconcentric nebuliser coupled to cyclonic or double pass spray chamber (MCN-C or MCN-DP, respectively) was investigated and compared when used for sample introduction to ICP-MS or ICP-OES. With ICP-OES, in axial viewing mode, intensity distributions across the radius of the plasma (radial intensity profiles) were determined for different spectral lines with Esum 1.85-15.41 eV to determine fundamental plasma properties for various matrices using Vulkan DIN and MCN-C. The results showed that with the MCN-C the ionisation temperature (Tion) was about the same across the measured region of the plasma (±3.0 mm) whereas with the Vulkan DIN the Tion was significantly lower in the centre of the plasma. A large deviation from local thermodynamic equilibrium, as well as deteriorated stability, was observed for the plasma when using the Vulkan DIN.

With ICP-MS noise power spectra (NPS) were generated to identify sources of noise. NPS showed that the magnitude of white noise for the tested sample introduction systems decreased in the following order: Vulkan DIN > DIHEN > MCN-C > MCN-DP. This order follows the decrease of mean droplet size and span of the size distribution, indicating that the white noise is caused by spatial and temporal non-uniform desolvation and ionisation. Another source of noise arose from the peristaltic pump and the magnitude of pump interference noise decreased in the following order: DIHEN > MCN-C/DP > Vulkan DIN. Mains power interference noise and 1/f noise were lower for the direct injection nebulisers compared to the spray chamber systems. The contribution or effects of these noise components on relative standard deviations of steady-state ion-count rate and isotope ratio measurements is discussed in this thesis.

Aerosols generated by the Vulkan DIN and the DIHEN were also directly characterised using Particle Dynamic Analysis. The Vulkan DIN produced particles with a mean diameter of ~30 µm and a size distribution between 2-80 µm. With the DIHEN the corresponding values were ~11 µm and 1-40 µm, respectively, with a few particles at 55-78 µm. The mean velocity of particles from the Vulkan DIN was ~10 m s-1 and from the DIHEN ~18 m s-1. The lower velocity allows longer residence time counteracting the effects of the larger droplet size.

Place, publisher, year, edition, pages
Umeå: Kemi, 2006. 40 p.
ICP, ICP-MS, ICP-OES, sample introduction, DIHEN, Vulkan DIN, non-spectral interferences, noise power spectra, analytical precision, plasma diagnostic parameters, particle dynamic analysis (PDA)
National Category
Analytical Chemistry
urn:nbn:se:umu:diva-671 (URN)91-7264-012-X (ISBN)
Public defence
2006-02-03, N350, Naturvetarhuset, Umeå Universitet, Umeå, 10:00
Available from: 2006-01-12 Created: 2006-01-12Bibliographically approved

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