Cadmium isotope ratio measurements in environmental matrices by MC-ICP-MS

Abstract

Various stages of an analytical method for high-precision cadmium (Cd) isotope ratio measurements by MC-ICP-MS (sample preparation, matrix separation, instrumental analysis and data evaluation) were critically evaluated and optimized for the processing of carbon-rich environmental samples. Overall reproducibility of the method was assessed by replicate preparation and Cd isotope ratio measurements in various environmental matrices (soil, sediment, Fe-Mn nodules, sludge, kidney, liver, leaves) and was found to be better than 0.1& (2s for d 114 Cd/ 110 Cd) for the majority of samples. Cd isotope ratio data for several commercially-available reference materials are presented and compared with previously published results where available. The method was used in a pilot study focusing on the assessment of factors affecting Cd isotope composition in tree leaves. A summary of results obtained for a large number (n > 80) of birch (Betula pubescenes) leaves collected from different locations in Sweden and through the entire growing season is presented and potential reasons for observed variability in Cd isotope composition are discussed. Seasonal dynamics of element concentrations and isotope compositions in leaves were also compared for Os, Pb, Zn and Cd.

Chromatographic Separation of Cd from Plants via Anion-Exchange Resin for an Isotope Determination by Multiple Collector ICP-MS

“…6 20 suggested that incomplete oxidation of carbon might interfere during ion-exchange separation and suggested to remove organic-rich matrices through ashing.…”

“…Metallic elements and residual resin-derived organic compounds lead to inaccurate Cd isotope results. 32 Pallavicicini et al 20 suggest ashing of organic-rich matrices. Wei et al 5,6 removed the organic matter of plants by HClO4.…”

“…Until now, only a few studies have been performed on the Cd isotopic compositions of plant samples, 5,6,20 which are rich in organic matter and metallic elements. Incomplete oxidation of carbon may disturb ion-exchange separation at later stages.…”

“…9,10 Cd isotope analyses have been applied in order to investigate the evolution of celestial bodies, [11][12][13] mineral genesis and material source, 7,14 paleo-ocean environments, [15][16][17][18][19] and environmental cadmium pollution sources. 3,4,8,[20][21][22] Furthermore, Wei et al 6 suggested that Cd isotope fractionation in Cd hyperaccumulator plants could apply new insights in the enrichment mechanisms.…”

“…As a rule, Cd recovery is required to be above 95% when sample standard bracketing (SSB) is used to correct the instrumental mass fractionation. 20,23,24 In addition, accurate measurements of the Cd isotope ratios are influenced by the isobaric interferences (i.e. 106 sufficiently from the samples.…”