isotope-analysis.com

Temporal variations spanning 0.4‰ for δ29Si and 0.8‰ for δ30Si of dissolved Si in the Kalix River were observed during the period, suggesting that the riverine Si input to the oceans cannot be considered to have a constant Si isotopic composition even on a short time scale. The results implicate biogeochemical Si-cycling via formation and dissolution of biogenic silica as major processes controlling the Si transport in boreal systems. The Si budget in the river system appeared to be controlled by relative Si accretions during high discharge events and relative Si depletions in the subarctic mountainous and lake dominated areas. There were also temporal variations in Si isotopic composition with accretion (relative Si contribution), accompanied by depletion of the heavier Si isotopes, while the opposite trend was observed during periods of riverine Si depletion. These isotope variations can be explained by release of plant derived silica, depleted in heavier Si isotopes, during the spring snowmelt. Further, increased volumetric contribution from the headwater and losses of Si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes. These conclusions are further verified by land cover analysis.

In both the Ob and Yenisey plumes suspended matter in the surface water had clearly negative values whereas samples close to the bottom showed values close to zero. It has previously been suggested that total Fe in river suspended matter (>0.2µm) in boreal regions is roughly a mixture of three phases, detrital particles (δ56Fe around zero), oxyhydroxide particles (δ56Fe positive) and C-Fe particles (δ56Fe negative). We suggest that the δ56Fe pattern observed in this study is the result of relatively rapid removal of detrital particles and Fe-oxyhydroxides, leaving a suspended fraction with negative values in the surface water in the outer parts of the freshwater plumes. Hence, during estuarine mixing of suspended particles heavy iron isotopes are deposited close to the river mouth, whereas light isotopes are exported to open ocean water.

To evaluate this hypothesis, seasonal isotopic pattern of boron (B) was investigated during spring and summer 2007 in a small stream draining a boreal forest area which was severely burnt in a major forest fire in the summer of 2006. Dissolved (< 0.22 µm) boron concentrations of the burnt area were significantly higher compared to a non-burnt reference stream, while 11B/10B ratios were significantly lower. Dissolved δ11B differences between the reference and the burnt area stream were found to be -9 to -22 ‰. We interpret the elevated B concentrations, accompanied by enrichment of 10B, in the burnt stream as wood and plant ash leaching of biogenic B from the burnt forest by surface run-off. Our results suggest that a boreal forest fire event significantly increases the leached amount of isotopically lighter B in the dissolved phase of stream run-off.

[1] Peltola & Åström (2006), Appl. Geochem. 21 (2006) 941- 948.

This study illustrates the high degree of difficulty inherent to these delta-scale measurements by 'routine' MC-ICPMS methodologies (in this case, three participants reported 55% of their results which were deemed accurate, and the other two reported none). The closer to unity the isotope ratio value the better the results became ('acceptable' results mostly for delta 7/6 parts per thousand and delta 7/8 parts per thousand measurements). This first experiment of its kind demonstrates that Pb delta-scale isotopic measurements by MC-ICPMS can be reliably carried out down to 0.05 parts per thousand levels (two participants delivered accurate results above this threshold systematically for delta/6 parts per thousand, delta 7/8 parts per thousand and delta 7/4 parts per thousand). Below this limit, at similar to 0.01 parts per thousand and similar to 0.03 parts per thousand levels, results are no longer consistent or reproducible and appear to be susceptible to a number of effects introducing error (such as short term changes in mass discrimination) which are either not well understood, or not controlled and/or not corrected for at a sufficiently low level of uncertainty. These results also suggest that 'routine' methods for absolute (calibrated) Pb-isotope ratio determination by MC-ICPMS produce relative combined uncertainties on results which are unlikely to be better than 0.05 parts per thousand (k = 2).

The long-term instrumental reproducibility, expressed as two standard deviations (2 sigma), for the isotopic reference material NBS28 (n=12) was 0.06%. for delta Si-29 and 0.12%. for delta Si-30. Results for the analyses of composite plant samples for the eight most prolific species in the boreal forest yielded a Surprisingly homogenous Si isotopic composition, expressed as delta Si-29 (expanded combined uncertainty) and delta Si-30, ranging from (-0.15 +/- 0.11)parts per thousand to (0.13 +/- 0.06)parts per thousand and (-0.31 +/- 0.08)parts per thousand to (0.22 +/- 0.13)parts per thousand , respectively. Isotopic and elemental analyses of local airborne particulate material suggest that the exogenous Si contribution varies between <1% and >70%. indicating that the potential surface contribution must be considered during Si Uptake studies. The present Study thus provides evidence that thorough appreciation of the forms of Si ill plants is all absolute requirement when assessing the plant impact oil the Si cycle via the difference in dissolution kinetics for phytoliths and lithogenic Si.

Measured Os concentrations in biological matrices increase in the order: small shrub leaves (blueberry and lingonberry)<= spruce needles <= mushrooms <= tree leaves <= pine needles < mosses << lichens. The concentrations found in three different species of plant were used to provide the first estimates of gaseous osmium tetroxide (OsO4) in the environment. Though the Os content of samples from Northeast Sweden does not differ significantly from matrix-matched international reference materials (not certified for Os) of abiotic origin, the estimates of gaseous OsO4 concentrations are roughly an order of magnitude higher than have been reported for particle-bound Os in other studies. The pronounced spatial variations between relatively closely situated sites in mean Os-187/Os-188 ratios for samples of the same species (presumably with the same dominating uptake mechanism) point to the presence of different local Os sources. This study therefore demonstrates that emissions of Os from automobile catalytic converters are not the only source of contemporary environmental contamination.

Based on isotope abundance ratios and similarities in spatial distributions between Os and chromium, smelters operated on chromium ores from Kemi deposits have shown to be the most important factor affecting the airbome Os burden in the region. The extent of the exposure is reflected by lichen concentrations near the source exceeding those from remote areas by a factor of 1000. Contributions from metal foundries processing iron, copper, lead and zinc ores can also be seen, though, because of lower Os concentrations in the feedstock, on a considerably lower scale. Masked by these industrial emissions in the studied area, the impact of Os originating from automotive catalytic converters cannot be resolved at present.

Abstract: Four long-lived neutron-deficient Th isotopes with atomic mass numbers 211 to 218 and abundances of (1-10)x10(-11) relative to Th-232 have been found in a study of naturally-occurring Th using inductively coupled plasma-sector field mass spectrometry. It is deduced that long-lived isomeric states exist in these isotopes. The hypothesis that they might belong to a new class of long-lived high spin super- and hyperdeformed isomeric states is discussed.

These methods include both acid and alkaline dissolution/fusion, Si separation using cation exchange, selective co-precipitation, and gas-source versus plasma-ionization (high and low resolution) mass-spectrometric techniques. The average delta Si-30 for Diatomite, IRMM-018, and Big-Batch are + 1.26 parts per thousand, -1.65 parts per thousand and -10.48 parts per thousand, respectively, with corresponding delta Si-9 values of + 0.64 parts per thousand, -0.85 parts per thousand and -5.35 parts per thousand for the same standards, respectively. For the most fractionated standard (Big-Batch), results demonstrate a kinetic mass-dependent fractionation effect for atomic Si (i.e., delta Si-29 similar to 0.51 x delta Si-30). There is almost no statistical difference between the mean values obtained by each participating laboratory, with the notable exception of the IRMM-018 standard. This effect could be caused by heterogeneity or contamination of this standard. The results for the other two standards indicate that data sets produced using any of the methods employed in this study will have similar precision and differences are limited to 0.2 parts per thousand in mean delta Si-30 values for a given sample between laboratories, or differences of 0.13 parts per thousand. in mean delta Si-29 values.

Combined with an ability to process sample sizes up to 2 g (up to 50 g if the organic matrix of biological or botanical samples is eliminated by ashing), materials with Os concentrations in the low, or even sub pg g(-1) range could be determined by this method. Given that two complete digestion/distillation systems were available for interchangeable use, throughputs of up to fifteen samples per 8 hour shift could be achieved. The method precision, evaluated as the long-term reproducibility of Os-187/Os-188 ratio measurements in a commercial Os reference sample containing 0.5 ng Os, was 0.16% relative standard deviation (RSD, 1s). The method has been applied to perform replicate Os-187/Os-188 ratio measurements on a suite of fifty reference materials of various origins and matrix compositions, with Os concentrations varying from < 0.1 pq g(-1) to) 100 ng g(-1), yielding an average precision of 3% RSD. Though none of the materials tested are certified for Os content or Os isotope composition, comparison of the obtained data with published Os isotope information for similar sample types revealed close agreement between the two. The method can also be used for the simultaneous, semi-quantitative determination of Os concentrations.

This data set allows identification of elements whose contents in caviar can be affected by salt addition as well as by contamination during production and packaging. Long-term method reproducibility was assessed for all analytes based on replicate caviar preparations/analyses and variations in element concentrations in caviar from different harvests were evaluated. The greatest utility for differentiation was demonstrated for elements with varying concentrations between brackish and freshwaters (e.g. As, Br, Sr). Elemental ratios, specifically Sr/Ca, Sr/Mg and Sr/Ba, are especially useful for authentication of vendace caviar processed from brackish water roe, due to the significant differences between caviar from different sources, limited between-harvest variations and relatively high concentrations in samples, allowing precise determination by modem analytical instrumentation. Variations in the Sr-87/Sr-86 ratio for vendace caviar from different harvests (on the order of 0.05-0.1%) is at least 10-fold less than differences between caviar processed from brackish and freshwater roe. Hence, Sr isotope ratio measurements (either by ICP-SFMS or by MC-ICP-MS) have great potential for origin differentiation. On the contrary, it was impossible to differentiate between Swedish caviar processed from brackish water roe and Finnish freshwater caviar based solely on Os-187/Os-188 ratios.

The precision of the method including filtration, digestion and instrumental determination ranges between 8% and 18% RSD for most elements on a dry weight basis. Higher recovery after acid digestion is found for some elements, probably because of volatilization or retention losses in the fusion procedure. Other elements show higher recovery after fusion, which is explained by more efficient decomposition of refractory mineral phases relative to the non-total acid digestion. Non-detectable concentrations of some elements are reported due to small differences between blank filter levels and the amounts of elements present on the filters after sampling. The method limits of detection range between 0.7 ng and 2.65 mu g, as estimated from the blank filter samples. These detection limits are 10-550 times higher compared to the corresponding instrumental limits of detection. The accuracy and bias of the overall analytical procedure was assessed from replicate analysis of certified reference materials. A critical evaluation of the instrumental capabilities of the ICP-QMS instrumentation in comparison with a double focusing sector field plasma mass spectrometry technique (ICP-SFMS) is also included. It was found that a modified microwave acid digestion procedure in combination with ICP-SFMS could replace ICP-AES determinations and fusion digestions for most of the investigated elements. Guidelines and limitations for this time- and labour- efficient procedure, offering accurate results for the majority of elements studied are discussed.

Data in this study indicate that these two types of colloids have different Fe-isotope composition. The Fe-C colloid has a negative delta Fe-56 value whereas the Fe-oxyhydroxide colloid is enriched in Fe-56.

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).

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.

Measurement of iron and zinc isotopes in human whole blood: Preliminary application to the study of HFE genotypes

Stenberg, A.; Malinovsky, D.; Öhlander, B.; Andrén, H.; Forsling, W.; Engström, L.-M.; Wahlin, A.; Engström, E.; Rodushkin, I.; Baxter, D.C.

J. Trace Elements Med. Biol.19 (2005) 55

Abstract: Multi-collector inductively coupled plasma – sector field mass spectrometry was applied to the measurement of Fe and Zn isotopes in human whole blood samples. For the Fe present in the blood of healthy adults, enrichment of the lighter isotopes relative to a standard material was observed, in agreement with earlier studies. The level of fractionation was

found to be lower in hemochromatosis patients exhibiting homozygous (C282Y/C282Y) mutation of the HFE gene. On
the one hand, this reinforces the hypothesis that Fe fractionation in blood decreases with enhanced dietary absorption. On the other hand, this contradicts predictions made on the basis of determinations of Fe fractionation in blood samples collected from subjects characterized by milder HFE mutations. In healthy subjects, the Zn in blood is depleted in lighter isotopes, consistent with the limited number of prior observations. As for Fe, the Zn isotopic composition exhibited a tendency toward lower levels of fractionation in the blood of subjects with hereditary hemochromatosis with homozygous mutation (C282Y/C282Y) of the HFE gene. The results therefore suggest that both Fe and Zn isotopic signatures in whole blood, at least to some extent, reflect polymorphisms in the HFE gene.

Performance of diffusive gradients in thin films for measurement of the isotopic composition of soluble Zn

Malinovsky, D.; Dahlqvist, R.; Baxter, D.C.; Ingri, J.; Rodushkin, I.

Anal. Chim. Acta 537 (2005) 401

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.

Effects of sample preparation and calibration strategy on accuracy and precision in the multi-elemental analysis of soil by sector-field ICP-MS

Engström, E.; Stenberg, A.; Baxter, D.C.; Malinovsky, D.; Mäkinen , I.; Pönni, S.; Rodushkin, I.

J. Anal. At. Spectrom. 19 (2004) 858

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 interlaboratory 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 tenfold 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.

Isotopic fractionation during diffusion of transition metal ions in solution

Rodushkin, I.; Stenberg, A.; Andrén, H.; Malinovsky, D.; Baxter, D. C.

Anal. Chem. 76 (2004) 2148

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 per mil. 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.

Isotopic variations of Zn in biological materials

Stenberg, A.; Andrén, H.; Malinovsky, D.; Engström, E.; Rodushkin, I.; Baxter, D. C.

Anal. Chem. 76 (2004) 3971

Abstract: Variations in the isotopic composition of Zn present in various biological materials were determined using high-resolution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), 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 ICP-MS 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-ICP-MS. The only other observed interference in the Cu and Zn mass range that could not be effectively eliminated by high-resolution multi-collection 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 s) 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.

Sources of mass bias and isotope ratio variation in multi-collector ICP-MS: optimization of instrumental parameters based on experimental observations

Andrén, H.; Rodushkin, I.; Stenberg, A.; Malinovsky, D.; Baxter, D.C.

J. Anal. At. Spectrom. 19 (2004) 1217

Abstract: In this work, several contributing factors to the observed mass bias in ICP-MS have been identified. Analyses of the isotopic compositions of B deposited on sampler and skimmer cones demonstrate enrichment of 10B on the former and 11B on the latter. Grounding the capacitive decoupling system magnified the level of 11B-enrichment on the skimmer cone more than four-fold. Thus supersonic expansion of the ion beam behind the sampler is confirmed to be an important source of mass bias. Isotopic analyses of Fe, Zn and Tl, 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 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.

Intercomparison of boron isotope and concentration measurements. Part II. Evaluation of results

Gonfianti, R.; Tonarini, S.; Gröning, M.; Adorni-Braccessi, A.; Al-Ammar, A. S.; Astner, M.; Bächler, S.; Barnes, R. M.; Bassett, R. L.; Cocherie, A.; Deyhle, A.; Dini, A.; Ferrara, G.; Gaillardet, J.; Grimm, J.; Guerrot, C.; Krähenbühl, U.; Layne, G.; Lemarchand, D.; Meixner, A.; Northington, D. J.; Pennisi, M.; Reitzerová, E.; Rodushkin, I.; Sugiura, N.; Surberg, R.; Tonn, S.; Wiedenbeck, M.; Wunderli, S.; Xiao, Y.; Zack, T.

Geostand. Newslett.27 (2003) 41

Abstract: The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration.

The materials were distributed to twenty seven laboratories – virtually all those performing geochemical boron isotope analyses in the world – which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11 B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution.

Separation of Fe from whole blood matrix for precise isotopic ratio measurements by MC-ICP-MS: a comparison of different approaches

Stenberg, A.; Malinovsky, D.; Rodushkin, I.; Andrén, H.; Pontér, C.; Öhlander, B.; Baxter, D. C.

J. Anal. At. Spectrom.18 (2003) 23

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 δ56 (–2.83 ± 0.06‰) and δ57 (–4.23 ± 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.

Separation of Fe from whole blood matrix for precise isotopic ratio measurements by MC-ICP-MS: a comparison of different approaches

Stenberg, A.; Malinovsky, D.; Rodushkin, I.; Andrén, H.; Pontér, C.; Öhlander, B.; Baxter, D. C.

J. Anal. At. Spectrom.18 (2003) 23

Performance of high resolution MC-ICP-MS for Fe isotope ratio measurements in sedimentary biological materials

Malinovsky, D.; Stenberg, A.; Rodushkin, I.; Andrén, H.; Ingri, J.; Öhlander, B.; Baxter, D. C.

J. Anal. At. Spectrom.18 (2003) 687

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 l-1.