| 1. |
- Andren, Henrik, et al.
(författare)
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Sources of mass bias and isotope ratio variation in multi-collector ICP-MS : optimization of instrumental parameters based on experimental observations
- 2004
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 19:9, s. 1217-1224
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Tidskriftsartikel (refereegranskat)abstract
- In this work, several contributing factors to the observed mass bias in inductively coupled plasma mass spectrometry (ICP-MS) have been identified. Analyses of the isotopic compositions of B deposited on sampler and skimmer cones demonstrate enrichment of [1][0]B on the former and [1][1]B on the latter. Grounding the capacitive discharge system to enhance sensitivity also magnified the level of [1][1]B enrichment on the skimmer cone more than four-fold. This supersonic expansion of the ion beam behind the sampler is confirmed to be an important source of mass bias. Isotopic analyses of the Fe, Zn and Ti leached from used extraction lenses yielded a linear relationship between the levels of lighter isotope depletion and mass ratio. Although consistent with the space-charge effect, the fact that isotopically-heavy deposits were found demonstrates that the ion beam diverges into a relatively wide solid angle in the field-free region behind the skimmer. This severely impairs transmission of, in particular, the lighter isotopes. For a wide range of elements (Li, B, Fe, Ni, Cu, Sb, Ce, Hf and Re), the magnitude of the mass bias was found to be affected by the sample gas flow rate, as well as the distance between the sampler and the end of the torch, i.e., the sampling depth, employed in the Neptune multi-collector ICP-MS instrument. Mathematical analysis of the profiles of intensity variations as a function of these instrumental parameters revealed that the response peaks closer to the torch for the heavier isotopes of all studied elements. Owing to this spatial non-coincidence, tuning for maximum intensity on either isotope will result in sampling from a region where even slight plasma instabilities will be translated into substantial variations in mass bias. Therefore, in-plasma processes also contribute to the degree and temporal stability of mass bias. In light of these findings, recommendations for optimizing multi-collector ICP-MS with respect to obtaining the highest possible precision are presented.
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| 2. |
- Andrén, Henrik
(författare)
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Studies of artificial mass bias in isotopic measurements by inductively coupled plasma mass spectrometry
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mass spectrometry, and especially inductively coupled plasma mass spectrometry (ICP-MS), suffers heavily from mass bias, or instrumental mass discrimination. The nett result of this effect is the preferential transmission, most often of heavier ions through the mass spectrometer. Most work regarding this phenomenon in ICP-MS dates back quite far, and has been interpreted in terms of the space-charge effect. This means that Coulombic forces acting on the beam of positively charged particles extracted from the ICP result in greater dissipation of lighter, and hence more mobile ions from the beam axis. In this work the importance of the space-charge effect as a universal explanation for mass bias is challenged by the results of high precision measurements of isotope ratios. Other than considering some commonly known sources of isotope ratio measurement bias, a not previously considered mechanism of isotopic fractionation has been investigated, i.e. diffusion in solution. It was established that, indeed, diffusion does lead to isotopic fractionation in solution, and although this is a long term process, may contribute to the minor isotopic variations observed in certain aquatic environments. Furthermore it was established that spectral interferences of argone oxide ions could be discerned from the ions of iron using high resolution ICP-MS, thus eliminating this potential source of artificial fractionation. Most significant was the discovery that the extent of mass bias varied throughout the volume of the plasma, and was further affected by sample characteristics, such as analyte concentration and acid strength. This identifies the plasma itself as the major source of instrumental mass discrimination. Varying the sampling position, i.e. the point at which ions are extracted from the plasma, not only affected the measured isotope ratios, but also the precision of such measurements. From these results, it is not recommended to measure at the sampling position providing maximum signal, since the variability in the isotope ratio is also at its' maximum there. Instead, the ions should be sampled from a point below the maximum, where the stability of the ratios will be better.
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| 3. |
- Andren, Henrik, et al.
(författare)
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Variations in instrumental mass discrimination
- 2004
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Ingår i: 2004 Winter Conference on Plasma Spectrochemistry. - Cambridge : Royal Society of Chemistry. ; , s. 329-
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Konferensbidrag (refereegranskat)
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| 4. |
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| 5. |
- Andren, Peter, et al.
(författare)
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Elastohydrodynamiska aspekter på vattenplaning : en litteraturstudie
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vattenplaning är ett allmänt känt begrepp och en fruktad situation förbilföraren. Att det finns likheter mellan smörjsituationen i ett kullager ochvattenplaning är däremot kanske förvånande. Denna litteraturstudie lyfterfram några resultat och fenomen som kan förklara likheter och skillnader.Syftet är att belysa dels vattenplaning som ett elastohydrodynamiskt fenomenoch dels ge tankar om hur den kunskap som finns inom smörjning av kullager,kuggväxlar och tätningar kanske kan användas vid studier av vattenplaningeller våtfriktionsproblem. Inledningsvis presenteras begreppenelastohydrodynamik, dynamisk och viskös vattenplaning. Därefter ges exempelpå experimentella och teoretiska studier av vattenplaning och till sist enkort inblick i de beräkningsmetoder som används för kullagersmörjning.Möjligheter och problem med att använda beräkningsteknik frånkullagersmörjning för att studera vattenplaning eller våtfriktion diskuteras.Var för sig är vattenplaning och elastohydrodynamik i maskinelement välutforskade områden men kombinationen är tämligen outforskad vilkettillsammans med de likheter som finns talar för fortsatta studier i ämnet.
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| 6. |
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| 7. |
- Malinovskiy, Dmitry, et al.
(författare)
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Performance of high resolution MC-ICP-MS for Fe isotope ratio measurements in sedimentary geological materials
- 2003
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Ingår i: Journal of Analytical Atomic Spectrometry. - 0267-9477 .- 1364-5544. ; 18:7, s. 687-695
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Tidskriftsartikel (refereegranskat)abstract
- High resolution MC-ICP-MS is used for the precise measurement of variations in the isotopic composition of Fe in ferromanganese concretions and sediments relative to IRMM-014 standard. The sensitivity for 56Fe in high resolution mode was 3 V per mg lm1 Fe, a figure that is comparable to those from other MC-ICP-MS instruments operated at low resolution. Incorporation of a guard electrode and the efficient ion transmission capabilities of the Neptune MC-ICP-MS instrument are responsible for the high sensitivity. It was observed that the use of HCl resulted in the formation of ClOH+, causing interference with 54Fe in particular. This acid has been preferred in some cases over HNO3 to minimize formation of ArN+, the major interferent for 54Fe. Using the high resolution mode of the Neptune, the nature of spectral interferences is unimportant as all are completely resolved and will not affect the accuracy of the determined Fe isotope ratios. As the instrument also provides flat-topped peaks, high resolution operation does not necessarily result in impaired precision, providing that higher concentrations are used to compensate for the loss in sensitivity compared with the low resolution mode. In the present work, external reproducibilities of 56Fe/54Fe and 57Fe/54Fe isotope ratios were better than 50 ppm (one standard deviation) at a concentration of 5 mg lm1. The level of instrumental mass discrimination observed for raw ratios drifted by as much as 0.09% per mass unit over a measurement session, but could be corrected on-line by simultaneous monitoring of the 62Ni/60Ni isotope ratio. Variations in the Fe concentrations or the acid strength of measurement solutions were found to affect the apparent mass discrimination. Increasing the Fe concentration caused a relative decrease in the raw 56Fe/54Fe and 57Fe/54Fe isotope ratios, thus ruling out the space charge effect as the explanation for this phenomenon. Instead, it is suggested that the larger dry aerosol particles formed at higher Fe concentrations are not completely vaporized until later in the plasma, thus reducing the relative rate of diffusional losses of lighter 54Fe from the central channel. However, application of on-line correction using Ni could adequately account for this effect. From the results for a variety of sedimentary geological materials, analysis of three-isotope data revealed that equilibrium fractionation of Fe occurred during deposition. To be able to distinguish between equilibrium and kinetic fractionation processes, it is imperative to collect accurate and precise data for the 56Fe/54Fe and 57Fe/54Fe isotope ratios. These requirements are readily fulfilled by applying high resolution MC-ICP-MS and on-line correction for instrumental mass discrimination using Ni.
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| 8. |
- Rodushkin, Ilia, et al.
(författare)
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Isotopic fractionation during diffusion of transition metal ions in solution
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:7, s. 2148-2151
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Tidskriftsartikel (refereegranskat)abstract
- Isotope ratios and elemental concentrations were measured in aqueous solutions sampled at varying distances from sources of Fe or Zn ions. The measurements reveal fractionation of isotopes resulting from pure diffusion in solution. Our data demonstrate that diffusion alone can cause changes in 56Fe/54Fe and 66Zn/64Zn isotope ratios in excess of -0.3”. These findings thus confirm previous suspicions that transport processes contribute to observed variations in isotopic compositions. Diffusion must therefore be considered when attempting to make inferences from isotope measurements on samples originating from aqueous systems where concentration gradients may develop.
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| 9. |
- Stenberg, Anna, et al.
(författare)
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Isotopic variations of Zn in biological materials
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:14, s. 3971-3978
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Tidskriftsartikel (refereegranskat)abstract
- Variations in the isotopic composition of Zn present in various biological materials were determined using high-resolution multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), following digestion and purification by anion exchange chromatography. To correct for differences in instrumental mass discrimination effects between samples and standards, Cu was employed as an elemental spike. Complementary analyses of Zn separates by sector field ICPMS instruments revealed that the concentrations of the majority of potentially interfering elements were reduced to negligible levels. Residual spectral interferences resulting from 35Cl16O2+, 40Ar14N2+, and 40Ar14N16O+ could be instrumentally resolved from the 67Zn, 68Zn, and 70Zn ion beams, respectively, during measurement by MC-ICPMS. The only other observed interference in the Cu and Zn mass range that could not be effectively eliminated by high-resolution multicollection resulted from 35Cl2+, necessitating modification of the sample preparation procedure to allow accurate 70Zn detection. Complete duplication of the entire analytical procedure for human whole blood and hair, as well as bovine liver and muscle, provided an external reproducibility of 0.05-0.12” (2) for measured 66/64Zn, 67/64Zn, and 68/64Zn values, demonstrating the utility of the method for the precise isotopic analysis of Zn in biological materials. Relative to the selected Zn isotopic standard, 66/64Zn values for biological samples varied from -0.60” in human hair to +0.56” in human whole blood, identifying the former material as the isotopically lightest Zn source found in nature to date.
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| 10. |
- Stenberg, Anna, et al.
(författare)
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Separation of Fe from whole blood matrix for precise isotopic ratio measurements by MC-ICP-MS: a comparison of different approaches
- 2003
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Ingår i: Journal of Analytical Atomic Spectrometry. - 0267-9477 .- 1364-5544. ; 18:1, s. 23-28
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Tidskriftsartikel (refereegranskat)abstract
- Anion-exchange and precipitation procedures for Fe separation from unspiked human whole blood after microwave digestion and ashing decomposition techniques were thoroughly evaluated in terms of Fe recoveries, decreases in matrix element concentrations and elimination of interfering species for subsequent Fe isotope ratio measurements by multi-collector ICP-MS. During isotope ratio measurements involving 54Fe, 56Fe and 57Fe, on-line mass discrimination correction using Ni isotopes was applied, significantly reducing uncertainties both within and between Fe sample runs. Despite Fe recoveries below 100% for all separation procedures studied, no artificial isotope fractionation was detected. The degree of Fe fractionation in a commercially available, whole blood sample (Trace Elements in Whole Blood, Level 1, Sero AS), expressed as 56i (m2.83 - 0.06‰) and 57i (m4.23 - 0.08‰) values relative to IRMM-014 Fe isotopic reference material, agrees well with previously published data. Of the tested separation procedures, precipitation using NH3 was found to be the most rapid and cost-effective method, yielding high Fe recovery and low levels of concomitant elements.
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