| 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. |
- 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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| 3. |
- Baxter, Douglas, et al.
(författare)
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Revised exponential model for mass bias correction using an internal standard for isotope abundance ratio measurements by multi-collector inductively coupled plasma mass spectrometry
- 2006
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 21:4, s. 427-430
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Tidskriftsartikel (refereegranskat)abstract
- An internal standard (IS) can be used to account for moderate, matrix-related shifts in mass bias using multi-collector inductively coupled plasma mass spectrometry through the empirical, linear relationship between measured isotope abundance ratios for different elements in ln-ln space. Unfortunately, erroneous mass bias corrected isotope abundance ratios may be returned by the model, requiring artificial adjustment of the true isotope abundance ratio of the IS. Although inadequate correction for peak tailing has been convincingly used to explain this problem, our analysis of the literature describing the development of the mass bias correction model using an IS reveals the presence of a source of systematic error. The origin of this error is purely mathematical and is eliminated in the revised model presented, in which mass bias corrected isotope abundance ratios are independent of the isotopic composition of the IS. An expression for computing the total combined uncertainty in the corrected ratio, incorporating contributions from the linear model, the isotopic reference material, and measurements of analyte element and IS in the sample, is also derived.
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| 4. |
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| 5. |
- Clayton, R.E, et al.
(författare)
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Fe isotope fractionation during the precipitation of ferrihydrite and transformation of ferrihydrite to goethite
- 2005
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 69:5, s. 667-676
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Tidskriftsartikel (refereegranskat)abstract
- Ferrihydrite and goethite are amongst the most important substrates for the sorption of contaminants in soil and other environmental media. Isotopic studies of the transition elements, particularly those that exhibit more than one oxidation state and show pH- and/or redox-sensitive behaviour at low temperatures, have been shown to be potentially useful present-day and past proxies for redox (or palaeoredox) conditions. We have made preliminary investigations of Fe isotope fractionation that take place during the formation of FeIII (oxy)hydroxides (FeIIIox) from an aqueous FeIII(NO3)3 solution (FeIIIaq) under laboratory conditions. We have attempted to keep the chemical system simple by excluding 'vital effects' and major changes in redox through the maintenance of abiotic conditions and use of FeIIIaq. Isotopic measurements (56Fe/54Fe, 57Fe/54Fe) of the FeIII(NO3)3 stock solution, the original ferrihydrite and the mixed ferrihydrite/goethite-supernatant FeIIIaq 'pairs' were carried out using a double focusing multicollector inductively coupled plasma mass spectrometer. The results reveal an apparent systematic variation indicating larger ΔFeIIIaq-FeIIIox with decrease in the ferrihydrite:goethite ratio, which reflects the time allowed for isotopic exchange. These values range from virtually zero (0.03‰) after 24 h to 0.30‰ after 70 h. In each FeIIIox-FeIIIaq 'pair' the lighter Fe isotope is partitioned into the FeIIIox, leaving the FeIIIaq isotopically heavier. The observed fractionation reflects isotopic exchange of Fe between the FeIIIox and FeIIIaq upon at least a two step transition of ferrihydrite to goethite.
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| 6. |
- Du, Andao, et al.
(författare)
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Preparation and certification of Re-Os dating reference materials: Molybdenites HLP and JDC
- 2004
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Ingår i: Geostandards and Geoanalytical Research. - 1639-4488 .- 1751-908X. ; 28:1, s. 41-52
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Tidskriftsartikel (refereegranskat)abstract
- Two Re-Os dating reference material molybdenites were prepared. Molybdenite JDC and molybdenite HLP are from a carbonate vein-type molybdenum-(lead)-uranium deposit in the Jinduicheng-Huanglongpu area of Shaanxi province, China. The samples proved to be homogeneous, based on the coefficient of variation of analytical results and an analysis of variance test. The sampling weight was 0.1 g for JDC and 0.025 g for HLP. An isotope dilution method was used for the determination of Re and Os. Sample decomposition and pre- concentration of Re and Os prior to measurement were accomplished using a variety of methods: acid digestion, alkali fusion, ion exchange and solvent extraction. Negative thermal ionisation mass spectrometry and inductively coupled plasma-mass spectrometry were used for the determination of Re and 187Os concentration and isotope ratios. The certified values include the contents of Re and Os and the model ages. For HLP, the Re content was 283.8 ± 6.2 µg g-1, 187Os was 659 ± 14 ng g-1 and the Re-Os model age was 221.4 ± 5.6 Ma. For JDC, the Re content was 17.39 ± 0.32 µg g-1, 187Os was 25.46 ± 0.60 ng g-1 and the Re-Os model age was 139.6 ± 3.8 Ma. Uncertainties for both certified reference materials are stated at the 95% level of confidence. Three laboratories (from three countries: P.R. China, USA, Sweden) joined in the certification programme. These certified reference materials are primarily useful for Re-Os dating of molybdenite, sulfides, black shale, etc. .
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| 7. |
- Engström, Emma, et al.
(författare)
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Effects of sample preparation and calibration strategy on accuracy and precision in the multi-elemental analysis of soil by sector field ICP-MS
- 2004
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 19, s. 858-866
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Tidskriftsartikel (refereegranskat)abstract
- Soil samples were prepared for multi-element analysis using HNO3 leaching or pseudo-total digestion with HNO3, HCl and HF in a microwave oven, both methods requiring 70 min heating time. Two calibration approaches for the soil characterization were also compared: external calibration, combined with internal standardization, and isotope dilution (ID) after appropriate spiking of the soils with a stable isotope mixture prior to sample preparation. Analyses were performed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS). Accurate total elemental concentrations were only obtained for Cd and P using both sample preparation methods in two certified reference materials, NIST SRM 2709 and CCRMP SO-2, as well as comparable values for a Finnish inter-laboratory soil. The pseudo-total digestion method also provided accurate results for As, Be, Co, Fe, Mn, Ni, Pb, Sb, Ti, V and Zn. For Cu in SO-2 and Cr in both certified reference materials, incomplete recoveries were always obtained. In the case of Cr, this is due to difficulties associated with the complete solubilization of refractory minerals.For a given final dilution factor, external calibration provides better limits of detection (LODs) than ID. As both methods of quantification yield results of essentially equivalent accuracy and precision, external calibration is to be preferred as a greater number of elements are amenable to analysis in a shorter measurement time. On the other hand, ID can be combined with matrix separation (NH3 precipitation was used here), allowing lower dilution factors to be used without deleterious effects on the instrumental performance. In particular, improved LODs could be obtained for Cd, Cu and Hg, primarily as a result of being able to introduce ten-fold more concentrated solutions from which the bulk of the matrix had been removed. For Cu and Ni, matrix separation almost eliminated Ti, and thus the formation of spectrally interfering TiO+ was completely suppressed. Potentially, the combination of ID and matrix separation would allow these elements to be determined without resorting to medium resolution measurement mode, again improving the LODs for the determination by ID-ICP-SFMS.
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| 8. |
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| 9. |
- Ingri, Johan, et al.
(författare)
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Iron isotope fractionation in river colloidal matter
- 2006
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 245:3-4, s. 792-798
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Tidskriftsartikel (refereegranskat)abstract
- Temporal variations in the iron isotopic composition, δ56Fe between − 0.13‰ and 0.31‰, have been measured in the suspended fraction in a Boreal river. The major mechanism behind these variations is temporal mixing between two types of particles–colloids, Fe-oxyhydroxides and Fe–C colloids. Data in this study indicate that these two types of colloids have different Fe-isotope composition. The Fe–C colloid has a negative δ56Fe value whereas the Fe-oxyhydroxide colloid is enriched in 56Fe. These two types of colloidal matter have different hydrogeochemical origin. The Fe–C colloid reaches the river during storm events when the upper sections of the soil profile (O and E horizons) are flooded by a rising water table. Colloidal Fe-oxyhydroxides reach the river via inflow and subsequent oxidation of groundwater enriched in dissolved Fe(II).
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| 10. |
- Malinovskiy, Dmitry, et al.
(författare)
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Aqueous transport and fate of pollutants in mining area: a case study of Khibiny apatite-nepheline mines, the Kola Peninsula, Russia : a case study of Khibiny apatite-nepheline mines, the Kola Peninsula, Russia
- 2002
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Ingår i: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 43:1-2, s. 172-187
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Tidskriftsartikel (refereegranskat)abstract
- Seven decades of mining activity on the Khibiny apatite-nepheline ore deposits and current large excavation volumes have resulted in elevated concentrations of total dissolved solids and metals in various waters near the mines. To assess the major sources of pollution inputs and fate of pollutants in watercourses draining the mine workings, snow cover, surface waters, and deposited and suspended sediments were sampled and analyzed. Water chemistry data showed that discharges of the mine wastewater are the main contributor to solute and metal loads in the streams. Atmospheric transport of metals and their accumulation in the snowpack account for a sharp increase in metal concentrations in stream waters during spring snowmelt. Data on bed and suspended sediments indicated that the streams have a low capacity of immobilization of metals. The dominant mechanism responsible for decrease in solutes in watercourses is dilution. The results demonstrated the necessity for remediation actions to address pollutant loads due to wastewater discharges
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| 11. |
- Malinovskiy, Dmitry, et al.
(författare)
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Determination of rhenium and osmium concentrations in molybdenite using laser ablation double focusing sector field ICP-MS
- 2004
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Ingår i: Journal of Geochemical Exploration. - : Elsevier BV. - 0375-6742 .- 1879-1689. ; 81:1-3, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- A technique for the in situ determination of Re and Os in molybdenite samples using direct solid sampling by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is described. The sample preparation is limited to molybdenite separation followed by grinding and pressing to pellets. For Re determination, the best results were obtained using external calibration in conjunction with internal standardization. Isotopes of both molybdenum and sulphur could be used as internal standards. This quantification approach provides precision levels generally better than 10% the relative standard deviation (RSD) with similar levels of accuracy. Os concentrations were derived from Re concentrations and measured isotopic ratios of intensities measured at masses 187 and 185, using W isotopes for on-line mass bias correction. As a rule, LA-ICP-MS results for Os agree with corresponding isotope dilution ICP-MS data to within 30%. Reproducibility is strongly dependent on the age of the molybdenite as well as on the precision of isotope ratio measurements, which in turn depend on Re and W concentrations. The proposed technique provides a rapid estimation of Re and Os concentrations for subsequent precise analysis by isotope dilution ICP-MS.
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| 12. |
- Malinovskiy, Dmitry, et al.
(författare)
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Determination of the isotopic composition of molybdenum in the bottom sediments of freshwater basins
- 2007
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Ingår i: Geochemistry International. - 0016-7029 .- 1556-1968. ; 45:4, s. 381-389
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of measurements of the Mo isotopic composition in the bottom sediments (BS) of freshwater basins. Mo isotopic ratios were measured using a multicollector inductively coupled plasma mass spectrometer (MC ICP MS). Efficient methods were used in this study for Mo separation from the elements of the sample matrix and correction for instrumental mass discrimination. This allowed us to achieve a high accuracy of 0.06, 0.08, and 0.14‰ (2 σ) for the measurement of 97Mo/95Mo, 98Mo/95Mo, and 100Mo/95Mo, respectively. The range of variations in Mo isotope ratios observed in the collected BS columns was ∼2.2‰ in terms of δ97Mo/95Mo. The results obtained here suggest that geochemical processes occurring during Mo migration with land water can change the isotopic composition of Mo. It is pointed out that the potential use of Mo isotopic systematics for reconstructions of redox conditions in seawater over the geologic past requires the quantification of isotopic effects of Mo accompanying its migration on land and the extent of possible variations in the isotopic composition of Mo entering the ocean.
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| 13. |
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| 14. |
- Malinovskiy, Dmitry
(författare)
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Fractionation of Fe and Zn isotopes : methods and some applications in aqueous geochemistry
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) has been used for the measurement of Fe and Zn isotope ratios in a variety of sample types including natural and synthetic waters, ferromanganese concretions, sediments and biological material. The focus of this PhD study was the development of analytical procedures for precise and accurate measurement of Fe and Zn isotope ratios by high resolution MC-ICPMS. The objective of the study has also been to complement the existing knowledge of Fe and Zn isotope fractionation that occurs due to fundamental physico- chemical processes such as oxidation-reduction and diffusion. Prior to the MC-ICPMS measurements, anion-exchange chromatography and precipitation procedures for purification of Fe and Zn have been thoroughly evaluated in terms of recoveries, decreases in matrix elements concentrations and elimination of interfering species. To correct for differences in instrumental mass discrimination effects between samples and standards, on-line normalisation procedure has been employed using Ni and Cu as elemental spikes for Fe and Zn isotope ratio measurements, respectively. It has been demonstrated that the on-line normalization in combination with sample-standard bracketing technique adequately correct for drift in the instrumental mass discrimination and reduce standard deviation of Fe and Zn isotope ratio measurements. External reproducibilities of 56Fe/54Fe and 66Zn/64Zn isotope ratios at typical concentrations of 2-5 mg l-1 were better than 50 ppm and 30 ppm (one standard deviation), respectively. Based on the established analytical methods Fe isotope variations have been explored at the oxic-anoxic interface of seasonally anoxic lake water and in deposited sediments under different redox conditions. The observed distribution of d56Fe values during redox cycling of Fe was found to be consistent with the model of equilibrium Fe isotope fractionation between co-existing aqueous Fe (II) species, such as Fe(OH)+, prior to oxidation. Different patterns of d56Fe values distribution for Fe oxide phase have been identified in the deposited sediments. In anoxic sediment column, where anoxic conditions were unchanged during the time of deposition, the d56 values are near-zero and rather invariant. In contrast, in sediment column of permanently oxygenated lake, where zone of the oxic-anoxic transition moved over time, d56 values for Fe oxides show large shifts, spanning the range of ~ 1.2‰. In light of the use of Fe isotope data in inference of geochemical pathways for Fe that may have occurred during primary precipitation and diagenesis, these data show the isotopic signature of Fe oxide phase that was accumulated due to precipitation of oxidized ferrous Fe flux. The measurements of Fe and Zn isotope ratios in aqueous solutions sampled at varying distances from sources of these ions revealed fractionation of the isotopes resulting from pure diffusion in solution. It has been demonstrated that diffusion alone can cause changes in 56Fe/54Fe and 66Zn/64Zn isotope ratio in excess of ~ 0.3‰. Furthermore, the effect of diffusion in hydrogels of diffusive gradients in thin films (DGT) samplers for measurements of isotopic composition of soluble metals as a possible source of fractionation has been investigated by using Zn as a test element. It has been shown that, provided quantitative elution is obtained, no fractionation of Zn isotopes due to the diffusion process is detectable within the reported precision of MC-ICPMS measurements. Consequently, DGT samplers are suitable for studies of the isotopic composition of soluble metals that are not affected by redox processes.
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| 15. |
- Malinovskiy, Dmitry, et al.
(författare)
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Fractionation of Fe isotopes as a result of redox process in a basin
- 2005
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Ingår i: Geohimiâ. - 0016-7525. ; 43:8, s. 878-885
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of a study of Fe isotope fractionation due to seasonal redox variations in water and bottom sediments (BS) of fresh-water basins. Fe isotopic ratios were measured using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). The investigation of suspended matter (SM) at the oxic-anoxic interface showed a significant positive shift in δ56Fe values between anoxic waters with dissolved Fe(II) and SM after Fe(II) oxidation and precipitation of Fe(III) oxides. Data on Fe content and isotope composition suggest that Fe(II) oxidation is accompanied by equilibrium Fe isotope fractionation. Potentials and limitations of the use of Fe isotope data for the reconstruction of pre-existing geochemical conditions in basins are outlined
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| 16. |
- Malinovskiy, Dmitry, et al.
(författare)
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Ion-specific isotopic fractionation of molybdenum during diffusion in aqueous solutions
- 2007
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 41:5, s. 1596-1600
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Tidskriftsartikel (refereegranskat)abstract
- Experiments modeling diffusion of Mo in aqueous solutions have been performed and, using multicollector ICP-MS, the ratios of the diffusivities of Mo isotopes, D97Mo/D95Mo, in aqueous solutions have been determined. Diffusion of MoO42- ions in solution was concomitant with Mo isotopic fractionation with D97Mo/D95Mo = 0.99988 ± 0.00004 (2σ for n = 3). In contrast, during diffusion of Mo polyanions, such as Mo7O246- and Mo8O264-, no measurable isotope fractionation has been found with D97Mo/D95Mo = 1.00000 ± 0.00002 (2σ for n = 3). These results indicate the need for due consideration to Mo speciation when attempting to interpret the role of diffusive fluxes in the formation of Mo isotopic signatures in nature. They also raise the possibility that the various chemical forms of other transition metals may be characterized by species-specific isotopic fractionation effects during physicochemical reactions.
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| 17. |
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| 18. |
- Malinovskiy, Dmitry, et al.
(författare)
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Molybdenum isotope ratio measurements on geological samples by MC-ICPMS
- 2005
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 245:1-3, s. 94-107
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Tidskriftsartikel (refereegranskat)abstract
- A method using multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for the precise measurement of Mo isotopic composition in geological samples has been developed. Purification of Mo for isotope ratio measurements was realized by ion-exchange chromatography using the chelating resin Chelex-100. This technique allows an efficient separation of Mo from an excess of Fe in samples and at the same time provides quantitative recovery of Mo. Instrumental mass discrimination is corrected by using Pd spiking and normalization to the 105Pd/104Pd ratio. Mo isotope ratios of samples are expressed in per mil relative to those of the bracketing in-house Mo standard. The long-term reproducibility at the two standard deviation level is 0.04, 0.06, 0.08 and 0.14‰ for 96Mo/95Mo, 97Mo/95Mo, 98Mo/95Mo and 100Mo/95Mo ratio measurements, respectively. The technique has been applied to measurement of the Mo isotopic composition of freshwater sediments and molybdenites. Mass-dependent variations in the isotopic composition of Mo spanning the range of 2.2‰ in terms of the 97Mo/95Mo ratio for two sediment columns from different redox environments have been resolved. These results show that Mo isotope effects induced by geochemical processes operating during weathering and transport of Mo to the oceans should be quantified in order to interpret global Mo isotope budget and make use of stable Mo isotopes as proxy for redox conditions in the geological past.
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| 19. |
- Malinovskiy, Dmitry, et al.
(författare)
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Performance of diffusive gradients in thin films for measurements of the isotopic composition of soluble Zn
- 2005
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 537:1-2, s. 401-405
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Tidskriftsartikel (refereegranskat)abstract
- The application of diffusive gradients in thin films (DGT) samplers for measurements of the isotopic composition of soluble Zn by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) was tested under laboratory conditions. The effect of diffusion in hydrogels as a possible source of fractionation was investigated by measuring Zn isotope ratios for different fractions of Zn accumulated by DGT and comparing with the bulk isotope composition of the solution. An important finding of this study is that, provided quantitative elution is obtained, no fractionation of Zn isotopes due to the diffusion process is detectable within the reported precision of MC-ICPMS measurements. Consequently, DGT samplers are suitable for studies of the Zn isotopic composition in natural waters.
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| 20. |
- 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
-
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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| 21. |
- Malinovskiy, Dmitry
(författare)
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Re-Os dating of molybdenite : new anlytical approaches using ICP-MS
- 2002
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, there has been a surge of interest in the direct dating of ore deposits using Re-Os geochronometer for the ore minerals themselves. Molybdenite has been or particular interest because it is a common ore mineral and is suitable for analysis by the Re-Os method due to relatively high concentration of both Re and Os. Until recently, reliable Re-Os dating of molybdenite was only possible using negative thermal ionisation mass spectrometry (NTIMS) involving time- and labour-consuming sample preparation procedures. Growing use of double focusing sector field inductively-coupled plasma mass spectometers, with their inherent capabilities for multielement analyses and large sample throuthput, demands the development of new analytical approaches for precise and accurate determination of Re and Os isotopes and dating of molybdenite. The major goal of this study was to develop a method for Re-Os dating of molybdenite using inductively copuled plasma mass spectrometry (ICP-MS) that can provide routine and precise quantification of Re and Os isotopes. As the method of isotope dilution (ID) is applied for accurate determination of isotope ratios in geochronological studies, the first attempts were made on the optimisation of Re and Os spike addition. In order to make a preliminary assessment of Os and Re concentrations in molybdenite and define the amounts of spikes necessary for precise isotope ratio determinations, the technique with minimum sample preparation - laser ablation ICP-MS (LA- ICP-MS) was used. It was demonstrated that LA-ICP-MS is a useful tool in the rapid, semi-quantitative determination of Re and Os concentrations in molybdenite. To improve the accuracy and precision of the LA-ICP-MS measurements, different calibration strategies were examined. External calibration with correction of instrumental drift by monitoring one of the major isotopes of molybdenite was found to be most effective for the determination of the Re concentration. Simple and robust mass discrimination correction using the 184W/182W isotope ratio performed in this LA study allows mathematical calculation of Os concentrations from measured 187(Re-Os)/185Re and tabulated 187Re185Re ratios with an accuracy sufficient for subsequent optimisation of the spike additions. Following addition of the spikes, the decomposition of molybdenite was studied. A novel two stage decomposition procedure in an autoclave was proved to allow complete spike-sample equilibration as a result of nitric and sulphuric attack under elevated temperature and pressure. The decomposition procedure also avoids the risk of explosion and extends the upper limit of the sample amount, these being the serious disadvantages of previously used techniques. Modification of the destillation procedure adopted for Os separation from the digest ensures high Os recovery and makes this procedure fast and optimally suitable for ICP-MS measurements. Re was separated from the matrix elements by using anion exchange. Minor modifications of this technique were also made that allowed more efficient Re separation from Mo. A significant achievement obtained in this study was the effective elimination of Os memory effects during ICP-MS measurement by using an ammonia solution. Optimisation of both the plasma conditions of the instrument using a shielded torch and the analyser scanning parameters resulted in improved sensitivity, providing the basis for accurate and precise Os isotope ratios measyrements. Advantages of the develpoed method are low cost of the equipment involved and its easy adaptation in chemical laboratories. Accuracy of the Re-Os dating was evaluated by replicate analyses of two moblybdenite reference materials (HLP-f and JDC). The Re-Os ages for these reference materials were quite reproducible (better than 0.92& RSD, 1 s, n=6) and compare well with the previously published data. Reproducibility typically obtained in the age determinations of mineral separates was about 1.5% RSD (1 s, n=5). This level of precision allows confident distinction between many geological events in the Precambrian.
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| 22. |
- Malinovskiy, Dmitry, et al.
(författare)
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Simplified method for the Re-Os dating of molybdenite using acid digestion and isotope dilution ICP-MS
- 2002
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Ingår i: Analytica Chimica Acta. - 0003-2670 .- 1873-4324. ; 463:1, s. 111-124
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Tidskriftsartikel (refereegranskat)abstract
- An analytical method was developed for Os-Re dating of molybdenite. The method is based on determination of Os and Re concentrations in molybdenite by isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS). Sample digestion and sample/spike equilibration were achieved by a two-stage autoclave-based procedure using a mixture of nitric and sulphuric acids. Os was separated from the sample digest by modified single-stage distillation of osmium tetraoxide (OsO4) using elevated temperature and on-line addition of hydrogen peroxide. OsO4(g) was trapped in a mixture of 0.05% thiourea in 0.05 M sodium hydroxide. An anion-exchange column was used to separate Re from excess Mo in the solution remaining after distillation. Os and Re isotope ratio measurements were performed by single-collector, double focusing inductively-coupled plasma mass spectrometry (ICP-MS) with on-line mass-bias correction. Typical instrumental precision was in the range 0.02-0.2% relative standard deviation (R.S.D.) depending on the analyte concentrations. Notorious Os memory effects in the ICP-MS introduction system were eliminated using 5% ammonia solution, both as matrix for final dilution of the trap mixture as well as for washing between the samples. The reproducibility of the entire analytical procedure was accessed by replicate dating of two molybdenite standards and three molybdenite separates, and was found to be in the range 0.87-1.52% R.S.D. Though accuracy of the method is limited by difficulties in evaluating exact concentration of Os in spike solution, ages obtained in the course of these work agrees well with previously published data.
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| 23. |
- Malinovskiy, Dmitry, et al.
(författare)
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Vanadium isotope ratio measurements in fruit-bodies of Amanita muscaria
- 2016
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Ingår i: Analytical Methods. - : Royal Society of Chemistry (RSC). - 1759-9660 .- 1759-9679. ; 8:30, s. 5921-5929
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Tidskriftsartikel (refereegranskat)abstract
- A new method has been developed for precise vanadium isotope ratio measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) in Amanita muscaria - a widespread toxic and hallucinogenic mushroom which is also known for its ability to bio-accumulate vanadium. Prior to isotope ratio measurements vanadium was separated from the sample matrix by anion-exchange chromatography with a single run of a sample solution through the anion-exchange column sufficient for the purification of vanadium. V-51/V-50 isotope ratio measurements were carried out in the high resolution mode of MC-ICPMS which allowed the separation of V-50(+) and V-51(+) ions from polyatomic interfering species, including sulphur-based ions. Iron was employed as an admixed internal standard and was found effective in correcting for the drift of instrumental mass bias. An important feature of the method was the use of a regression model in data reduction. The Plackett-Burman factorial design was used for ruggedness testing and showed that normalisation to the Fe-56/Fe-54 isotope ratio of the internal standard significantly improved the repeatability of the results. The combined standard uncertainties of delta V-51 values determined for samples of the mushroom ranged from 0.28 parts per thousand to 0.42 parts per thousand. delta V-51 values for the samples collected in geographically different locations varied from -0.7 parts per thousand to 1.7 parts per thousand, suggesting V-51/V-50 isotope ratio measurements as a useful tool for identifying the origin of Amanita muscaria in tasks concerned with counteracting the abuse of hallucinogenic mushrooms and in studies on the biochemistry of vanadium.
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| 24. |
- Malinovskiy, Dmitry, et al.
(författare)
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Variations in the isotopic composition of molybdenum in freshwater lake systems
- 2007
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 236:3-4, s. 181-198
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Tidskriftsartikel (refereegranskat)abstract
- Variations in molybdenum isotopic composition, spanning the range of ≈ 2.3‰ in the terms of 97Mo/95Mo ratio, have been measured in sediment cores from three lakes in northern Sweden and north-western Russia. These variations have been produced by both isotopically variable input of Mo into the lakes due to Mo isotopic heterogeneity of bedrock in the drainage basins and fractionation in the lake systems due to temporal variations in limnological conditions. Mo isotope abundances of bedrock in the lake drainage basins have been documented by analysis of Mo isotope ratios of a suite of molybdenite occurrences collected in the studied area and of detrital fractions of the lake sediment cores. The median δ97Mo value of the investigated molybdenites is 0.26‰ with standard deviation of 0.43‰ (n = 19), whereas the median δ97Mo value of detrital sediment fractions from two lakes is - 0.40‰ with standard deviation of 0.36‰ (n = 15). The isotopic composition of Mo in the sediment cores has been found to be dependent on redox conditions of the water columns and the dominant type of scavenging phases. Hydrous Fe oxides have been shown to be an efficient scavenger of Mo from porewater under oxic conditions. Oxidative precipitation of Fe(II) in the sediments resulted in co-precipitation of Mo and significant authigenic enrichment at the redox boundary. In spite of a pronounced increase in Mo concentration associated with Fe oxides at the redox boundary the isotopic composition of Mo in this zone varies insignificantly, suggesting little or no isotope fractionation during scavenging of Mo by hydrous Fe oxides. In a lake with anoxic bottom water a chironomid-inferred reconstruction of O2 conditions in the bottom water through the Holocene indicates that increased O2 concentrations are generally associated with low δ97Mo/95Mo values of the sediments, whereas lowered O2 contents of the bottom water are accompanied by relatively high δ97Mo/95Mo values, thus confirming the potential of Mo isotope data to be a proxy for redox conditions of overlying waters. However, it is pointed out that other processes including input of isotopically heterogeneous Mo and Mn cycling in the redox-stratified water column can be a primary cause of variations in Mo isotopic compositions of lake sediments.
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| 25. |
- Rodushkin, Ilya, et al.
(författare)
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Analyte- and matrix-dependent elemental response variations in laser ablation inductively coupled plasma mass spectrometry : Part 2. Implications for multi-element analyses
- 2002
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 17:10, s. 1231-1239
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Tidskriftsartikel (refereegranskat)abstract
- Given that laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has the potential to directly determine the concentrations of some 80 elements in solid samples, the fact that most applications are limited to considerably smaller numbers of analytes is indicative of the inherent problems with calibration. These stem from elemental response variations, both between analytes in any given sample and between matrices for any given analyte. Although response variations are often attributed to differences in ablation or transport efficiencies, there have also been indications that some degree of elemental fractionation may occur in the ICP. The results of the present investigations demonstrate that the ICP is the predominant source of fractionation, and thus response variations are related to the thermodynamic properties of the elements and their host particles. By studying analyte response as a function of carrier gas flow rate (so called flow rate plots) in 16 matrices, patterns in the behaviour of the elements in LA-ICP-MS could be clearly discerned and used for classification. Three groups of elements displaying consistent behavioural patterns over all matrices were identified from these studies: Group A, comprising refractory elements with high oxide bond dissociation enthalpies; Group B, including the rare and heavier alkaline earth (Ca, Sr, Ba) elements; and Group C, consisting of volatile or low mass elements. As each group exhibits decidedly different optimum flow rates and flow rate plot shapes which, with the exception of the group C elements, also depend on the matrix, the utility of LA-ICP-MS for multi-element analyses is severely compromised. In fact, quantitative determination of a wide range of analytes demands that calibration factors be established for at least one element from each group, as well as for all elements that could not be satisfactorily classified. This classification may serve as a guide in the selection of suitable internal standards for LA-ICP-MS, at least for certain groups of analytes. Examples are also given showing how flow rate plots can be employed to predict the adequacy of selected internal standards or solid standard materials for calibration
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| 26. |
- Rodushkin, Ilya, et al.
(författare)
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Analyte- and matrix-dependent elemental response variations in laser ablation inductively coupled plasma mass spectrometry : Part 1. The roles of plasma and ion sampling conditions
- 2002
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 17:10, s. 1223-1230
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Tidskriftsartikel (refereegranskat)abstract
- Elemental response variations as a function of carrier gas flow rate in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were studied for a wide range of analytes. The effects of rf power, focus lens settings, thermodynamic properties of analytes and sample matrix were thoroughly examined. It was found that, with the experimental set-up used for this work, processes occurring in the ICP, rather than during ablation and transport, play the decisive role in determining the shapes of flow rate plots observed with LA. Responses for analytes of lower nominal masses and vaporization enthalpies peak at consistently higher flow rates (1.15 1 min-1) than other elements, independent of matrix. On the other hand, the magnitude of the maximum sensitivity is matrix dependent, even for these elements. Involatile elements display much broader maxima at considerably lower flow rates; the more refractory the matrix, the lower the optimum flow rate. This behaviour is consistent with the residence time in the ICP necessary to maximize the efficiency of analyte ion production. The existence of inter-elemental differences in the locations of zones of maximum ion densities formed in the ICP can thus be related to the times required for vaporization of any given analyte from the particles produced by LA. Such differences may be responsible for numerous fractionation effects mentioned in the LA literature. It is also demonstrated that the ion sampling process can affect the shapes of the flow rate plots, potentially shifting the apparent position of the optimum flow rate and confounding the interpretation of inter-element response differences.
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| 27. |
- 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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| 28. |
- 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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| 29. |
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| 30. |
- 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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