An analytical method for precise determination of the cadmium isotopic composition in plant samples using multiple collector inductively coupled plasma mass spectrometry

Abstract

Isotope techniques can be applied to discover the migration and transformation of metal elements in plants. However, only a few studies on Cd isotopes in plants have been carried out so far. In this study, an optimized analytical method consisting of digestion, purification and determination of Cd isotopes in plants was developed. Three Cd standard solutions as well as four plant species (Solanum nigrum, Ricinus communis, Cyperus alternifolius and Pteris vittata), which were grown in soil or hydroponic cultures, were repeatedly analyzed for Cd isotopes using Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS). The factors that affected the accuracy of Cd isotopic determination, such as isobaric interference and instrumental mass fractionation, have been carefully evaluated and corrected. The purification procedure yielded a Cd recovery of not less than 95% and effectively eliminated the spectral interference of Pd, In and Sn as well. The analysis of pure Cd standard materials showed accurate isotope values, which matched with the results of previously published methods. This technique provided an average long-term external reproducibility of ±0.09‰ for δ^114/110Cd (2SD). The overall δ^114/110Cd values of four plant species ranged from −0.39‰ to −0.08‰ and provided direct evidence for Cd isotopic fractionation in herbaceous plants.