Precise determination of cadmium and lead isotopic compositions in river sediments

A method for the accurate determination of Cd and Pb isotope compositions in sediment samples is presented. Separation of Cd and Pb was designed by using an anionic exchange chromatographic procedure. Measurements of Cd isotopic compositions were carried out by multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS), by using standard-sample bracketing technology for mass bias correction and Pb isotopic ratios were determined by thermal ionization mass spectrometry (TIMS). The factors that affect the accurate and precise Cd isotope compositions analysis, such as instrumental mass fractionation and isobaric interferences, were carefully evaluated and corrected. The Cd isotopic results were reported relative to an internal Cd solution and expressed as the delta(114/110)Cd. Five Cd reference solutions and one Pb standard were repeatedly measured in order to assess the accuracy of the measurements. Uncertainties obtained were estimated to be lesser than 0.11 per thousand (2s) for the delta(114/110)Cd value. Analytical uncertainties in 2s for Pb isotopic ratios were better than 0.5 per thousand. The method has been successfully applied to the investigation of Cd and Pb isotope compositions in sediment samples collected from North River in south China.