Determination of Chromium and Mercury in Sediments by Isotope Dilution-Inductively Coupled Plasma Mass Spectrometry

The contents of Cr and Hg in sediments were determined by isotope dilution-inductively coupled plasma mass spectrometry (ID-ICP-MS). Primary standard solutions of Cr and Hg were used to calibrate the concentrations of ⁵³Cr and ²⁰²Hg enriched isotope, respectively. The samples were mixed with ⁵³Cr and 202Hg spikes and digested by acid in PTFE vessel separately. Data acquisition parameters were optimized in the process of measurement by ICP-MS. Interference from sample matrix was explored, and the results of Cr under the two modes of H₂ and He were compared. In order to avoid the memory effect to the ratio determination of Hg, 5 mg/L EDTA, 2.5 mg/L Au solution and 3% HNO₃ were used to flush piping system by turns. The calculation results by ratio of ²⁰⁰Hg/²⁰²Hg and ¹⁹⁹Hg/²⁰²Hg were compared. The results showed that accurate isotope ratio is obtained and the matrix effects are eliminated when the integration time is 0.5 s and after a proper dilution to the sample. The modes of H₂ and He are appropriate for the determination of Cr in the sample, and the contents of Hg results from ²⁰⁰Hg/²⁰²Hg and ¹⁹⁹Hg/²⁰²Hg have no significant differences. Method verification were made by the NIST2709a certified reference material, the results showed good coincidence with the certified values. The contents of Cr and Hg are 81.73 mg/kg and 0.471 mg/kg, and the RSDs are 0.35% and 0.99%, respectively. The method has high accuracy and good precision, and it is suitable for the determination of chromium and mercury in sediment and soil samples.