Emma Engström

Isotopic analysis of the metabolically relevant transition metals Cu, Fe and Zn in human blood from vegetarians and omnivores using multi-collector ICP-mass spectrometry

Multi-collector ICP-mass spectrometry (MC-ICP-MS) was used for the isotopic analysis of Cu, Fe and Zn, isolated from human whole blood. For chromatographic isolation of these elements, the method first described by Marechal, Telouk and Albarede (Chem. Geol., 1999, 156, 251–273) and relying on the use of AG MP-1 strong anion exchange resin was further tailored and subsequently validated. It was shown that all three target elements could be obtained in pure form and with quantitative recovery from Seronorm whole blood reference material. MC-ICP-MS isotope ratio measurement conditions were optimized so as to avoid the influence of spectral overlap and the capabilities of several methods to correct for instrumental mass discrimination were compared. The method developed was then applied to a set of whole blood samples from supposedly healthy volunteers (reference population). For Fe, the by now well-known difference in isotopic composition between blood from male and female individuals was confirmed. The isotopic composition of Zn in whole blood was assessed to be governed by the diet as a significant difference could be established between blood from vegetarians and from omnivores, respectively. For the isotopic composition of Cu, interpretation of the results is more challenging, as neither gender, nor diet seems to have a significant influence, but the combined influence of both factors may show an effect.

Isotope abundance ratio measurements by inductively coupled plasma-sector field mass spectrometry

This tutorial reviews fundamental aspects of isotope abundance ratio measurement by inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). After a synopsis of the scope of isotope abundance ratio measurement and a summary introduction to the factors affecting precision and accuracy, attention is turned to noise sources. Detailed theory behind Poisson or counting statistics and plasma flicker noise components is given, since much of the observed imprecision can be attributed to these sources. Using single collector instruments, ion beams from different isotopes are sampled in rapid sequence, and so ratioing of the signals will be subject to fluctuations derived from intensity variations, i.e., flicker noise. It is demonstrated that flicker noise can, under specified circumstances, become the limiting factor for the attainable precision. Furthermore, the practice of partitioning dwell times, ostensibly to optimize precision based on isotopic abundances and assumed Poisson statistics, is shown to be flawed and actually requires accounting for flicker noise. In addition to random uncertainty, various offset factors may contribute to systematic error in measured isotope abundance ratios. Two of these, namely mass scale shift and spectral interferences are ameliorated using ICP-SFMS. The former is eliminated when operating under conditions providing flat-topped peaks, such that the minor drift in mass calibration typical of the technique becomes inconsequential and the intensity remains the same. Isotope abundance ratio measurements are subject to three further important offset factors. First is abundance sensitivity, which quantifies the extent of peak tailing to neighboring masses and can present a considerable source of offset. Second is mass bias, resulting from the fact that all sector field devices exhibit increasing sensitivity with ion mass, and various empirical methods used to correct for this effect are compared and contrasted. Third is detector dead time, which affects mass spectrometers equipped with ion counting systems. Although a well-understood phenomenon, all current methods for determining the dead time on the basis of experimentally measured isotope abundance ratios are likely to yield biased estimates. Finally, the capabilities of ICP-SFMS for the determination of isotope abundance ratios are placed in perspective by making a brief comparison with other techniques.

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

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. n 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.

The role of bacterial consortium and organic amendment in Cu and Fe isotope fractionation in plants on a polluted mine site

Copper and iron isotope fractionation by plant uptake and translocation is a matter of current research. As a way to apply the use of Cu and Fe stable isotopes in the phytoremediation of contaminated sites, the effects of organic amendment and microbial addition in a mine-spoiled soil seeded with Helianthus annuus in pot experiments and field trials were studied. Results show that the addition of a microbial consortium of ten bacterial strains has an influence on Cu and Fe isotope fractionation by the uptake and translocation in pot experiments, with an increase in average of 0.99u2009‰ for the δ65Cu values from soil to roots. In the field trial, the amendment with the addition of bacteria and mycorrhiza as single and double inoculation enriches the leaves in 65Cu compared to the soil. As a result of the same trial, the δ56Fe values in the leaves are lower than those from the bulk soil, although some differences are seen according to the amendment used. Siderophores, possibly released by the bacterial consortium, can be responsible for this change in the Cu and Fe fractionation. The overall isotopic fractionation trend for Cu and Fe does not vary for pot and field experiments with or without bacteria. However, variations in specific metabolic pathways related to metal–organic complexation and weathering can modify particular isotopic signatures.

On the application of ICP-MS techniques for measuring uranium and plutonium: a Nordic inter-laboratory comparison exercise

Inductively coupled plasma mass spectrometry (ICP-MS) techniques are widely used for determination of long-lived radionuclides and their isotopic ratios in the nuclear fields. Uranium (U) and Plutoniumxa0(Pu) isotopes have been determined by many researchers with ICP-MS due to its relatively high sensitivity and short measurement time. In this work, an inter-laboratory comparison exercise among the Nordic countries was performed, focusing on the measurement of U and Pu isotopes in certified reference materials by ICP-MS. The performance and characters of different ICP-MS instruments are evaluated and discussed in this paper.

Seasonal shift of diet in bank voles explains trophic fate of anthropogenic osmium

Diet shifts are common in mammals and birds, but little is known about how such shifts along the food web affect contaminant exposure. Voles are staple food for many mammalian and avian predators. There is therefore a risk of transfer of contaminants accumulated in voles within the food chain. Osmium is one of the rarest earth elements with osmium tetroxide (OsO4) as the most toxic vapor-phase airborne contaminant. Anthropogenic OsO4 accumulates in fruticose lichens that are important winter food of bank voles (Myodes glareolus). Here, we test if a) anthropogenic osmium accumulates in bank voles in winter, and b) accumulation rates and concentrations are lower in autumn when the species is mainly herbivorous. Our study, performed in a boreal forest impacted by anthropogenic osmium, supported the hypotheses for all studied tissues (kidney, liver, lung, muscle and spleen) in 50 studied bank voles. In autumn, osmium concentrations in bank voles were even partly similar to those in the graminivorous field vole (Microtus agrestis; n=14). In autumn but not in late winter/early spring, osmium concentrations were generally negatively correlated with body weight and root length of the first mandible molar, i.e. proxies of bank vole age. Identified negative correlations between organ-to-body weight ratios and osmium concentrations in late winter/early spring indicate intoxication. Our results suggest unequal accumulation risk for predators feeding on different cohorts of bank voles.