Epov Vladimir N, Rodriguez-Gonzalez Pablo, Sonke Jeroen E, Tessier Emmanuel, Amouroux David, Bourgoin Laurence Maurice, Donard Olivier F X
LCABIE, IPREM, CNRS UMR-5254, Pau University, 2 Avenue du President Angot, Pau, 64053, France.
Anal Chem. 2008 May 15;80(10):3530-8. doi: 10.1021/ac800384b. Epub 2008 Apr 11.
This work presents the simultaneous online determination of the isotopic composition of different Hg species in a single sample by the hyphenation of gas chromatography (GC) with multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS). With the use of commercially available instrumentation, precise and accurate species-specific Hg isotope delta values (per mil deviation of the Hg isotope ratio in the sample relative to a reference standard) have been obtained online from consecutive GC transient signals. The use of isothermal temperature programs to extend the elution of the Hg species, the proper selection of the peak integration window, as well as the preconcentration of real samples are critical to provide optimal counting statistics. Also, isotope ratio drift during transient signal elution was overcome by introducing a mixed Hg(II) and MeHg standard bracketing scheme and expressing all results using the delta-notation relative to SRM NIST-3133. Using the proposed methodology, we have obtained an external 2SD precision of 0.56 per thousand for delta (202)Hg that is more than 10 times smaller than the overall Hg stable isotope variation thus far observed in terrestrial samples. The measurement of species-specific Hg isotopic composition relative to SRM NIST-3133 has been validated versus two other analytical techniques, i.e., conventional nebulization (CN) of Hg(II) solution and cold vapor (CV) generation of Hg (0) vapor. A good agreement between the species-specific delta values obtained by the different techniques has been obtained in secondary fractionated reference standard (UM-Almaden) and environmental matrixes, i.e., BCR-CRM 464 (tuna fish) and IAEA-085 (human hair). The results show mass-dependent and mass-independent fractionation in environmental samples, i.e., mass-independent fractionation of odd isotopes (199)Hg and (201)Hg in tuna fish was observed. This methodology provides new possibilities for the future study of species-specific stable isotope geochemistry of Hg and other trace metals.
本研究通过气相色谱（GC）与多接收电感耦合等离子体质谱（MC-ICPMS）联用，实现了在单个样品中同时在线测定不同汞物种的同位素组成。利用市售仪器，已从连续的GC瞬态信号中在线获得了精确且准确的物种特异性汞同位素δ值（样品中汞同位素比值相对于参考标准的千分偏差）。采用等温温度程序延长汞物种的洗脱时间、正确选择峰积分窗口以及对实际样品进行预浓缩，对于提供最佳计数统计至关重要。此外，通过引入混合Hg(II)和甲基汞标准的夹逼方案，并使用相对于SRM NIST-3133的δ符号表示所有结果，克服了瞬态信号洗脱期间的同位素比值漂移。使用所提出的方法，我们获得了δ(202)Hg的外部2SD精度为0.56‰，这比迄今为止在陆地样品中观察到的总汞稳定同位素变化小10倍以上。相对于SRM NIST-3133的物种特异性汞同位素组成的测量已通过与另外两种分析技术进行验证，即Hg(II)溶液的传统雾化（CN）和Hg(0)蒸气的冷蒸气（CV）生成。在二次分级参考标准（UM-阿尔马登）和环境基质（即BCR-CRM 464（金枪鱼）和IAEA-085（人发））中，不同技术获得的物种特异性δ值之间取得了良好的一致性。结果表明环境样品中存在质量依赖和质量非依赖分馏，即在金枪鱼中观察到奇数同位素(199)Hg和(201)Hg的质量非依赖分馏。该方法为未来汞和其他痕量金属的物种特异性稳定同位素地球化学研究提供了新的可能性。
