同位素稀释-电感耦合等离子体质谱法测定沉积物中铬和汞

采用同位素稀释-电感耦合等离子体质谱法（ID-ICP-MS）测定沉积物中铬和汞，分别以铬、汞单元素溶液标准物质标定⁵³Cr和²⁰²Hg浓缩同位素，将稀释剂与样品混合均匀后，加酸进行消解。对质谱测定过程的数据采集参数进行优化，探究基体效应以及H2和He两种模式对铬测定的影响。为防止汞的记忆效应干扰比值的测定，采用5 mg/L EDTA、2.5 mg/L Au溶液和3%硝酸交替冲洗管路系统，分别测定了²⁰⁰Hg/²⁰²Hg和¹⁹⁹Hg/²⁰²Hg两组比值，并比较测定结果。结果显示：积分时间为0.5 s时，同位素比值的测定精密度较好，对测定样品进行稀释能够消除质谱及基体效应干扰。H₂和He模式均适用于该类样品中铬的测定，²⁰⁰Hg/²⁰²Hg和¹⁹⁹Hg/²⁰²Hg两组比值对汞的测定结果无显著性差异，沉积物中铬和汞含量分别为81.7 mg/kg和0.471 mg/kg，相对标准偏差分别为0.35%和0.99%。采用美国NIST2709a标准物质进行方法验证，验证结果与标准值一致。该方法准确度高、精密度良好，适用于沉积物、土壤等基体样品中铬和汞的高准确度测定。

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.