Isotope dilution inductively coupled plasma mass spectrometry to measure the bioaccessible fraction of chromium in sediments

Abstract

The bioaccessible fraction of chromium in marine sediments is determined first time using isotope dilution Inductively Coupled Plasma Mass Spectrometry (ID-ICPMS). A diluted hydrochloric acid solution enriched with 53Cr was used as extractant to achieve isotope equilibration with the mass fraction of Cr extracted, using ultrasonic probe agitation. The parameters affecting trueness and precision were evaluated and/or corrected to minimize the errors; namely: detector dead time, spectral interferences, mass discrimination factor and selection of the optimum sample/spike ratio. The fraction of Cr measured correlated well with the sum of the certified contents of the 3-step sequential extraction of the Standards, Measurements and Testing Programme, SM&T, when analysing the BCR-701 sediment. The method provided good reproducibility (1.4% RSD) and low detection limit, 16.7 ng g−1. Three additional reference sediments with certified total chromium contents were also analysed as quality control checks. The total uncertainty budget of the procedure was estimated following the EURACHEM Guide propagating together the individual uncertainty components of the isotope dilution, obtaining a satisfactory relative expanded uncertainty of 1.9%. The analysis of sediments from two rias of Galicia (Arousa and Vigo, Northwest Spain) demonstrated the applicability of the proposed methodology.