Research Institute for Pesticides and Water, Universitat Jaume I, E-12071, Castelló, Spain.
Anal Chem. 2010 Apr 1;82(7):2773-83. doi: 10.1021/ac9027033.
This work demonstrates, for the first time, the applicability of multiple spiking isotope dilution analysis to molecular mass spectrometry exemplified by the speciation analysis of mercury using GC(EI)MS instrumentation. A double spike isotope dilution approach using isotopically enriched mercury isotopes has been applied for the determination of inorganic mercury Hg(II) and methylmercury (MeHg) in fish reference materials. The method is based on the application of isotope pattern deconvolution for the simultaneous determination of degradation-corrected concentrations of methylmercury and inorganic mercury. Mass isotopomer distributions are employed instead of isotope ratios to calculate the corrected concentrations of the Hg species as well as the extent of species degradation reactions. The isotope pattern deconvolution equations developed here allow the calculation of the different molar fractions directly from the GC(EI)MS mass isotopomer distribution pattern and take into account possible impurities present in the spike solutions employed. The procedure has been successfully validated with the analysis of two different certified reference materials (BCR-464 and DOLT-4) and with the comparison of the results obtained by GC(ICP)MS. For the tuna fish matrix (BCR-464), no interconversion reactions were observed at the optimized conditions of open focused microwave extraction at 70 degrees C during 8 min. However, significant demethylation was found under the same conditions in the case of the certified dogfish liver DOLT-4. Methylation and demethylation factors were confirmed by GC(ICP)MS. Transformation reactions have been found to depend on the sample matrix and on the derivatization reagent employed. Thus, it is not possible to recommend optimum extraction conditions suitable for all types of matrices demonstrating the need to apply multiple spiking methodologies for the determination of MeHg and Hg(II) in biological samples. Double spike isotope dilution analysis methodologies using widespread GC(EI)MS instrumentation are proposed here for the routine analysis of inorganic mercury and methylmercury in fish samples. The estimated method detection limits were below 10 ng g(-1) for both mercury species. Precision was evaluated for the concentrations present in the certified reference materials (CRMs) which vary from 0.1 to 5 microg g(-1), achieving values of coefficients of variation ranging from 7% to 2%. The concentrations obtained in both CRMs analyzed were in excellent agreement with the certified values, demonstrating the accuracy of the method at these concentration levels.
这项工作首次展示了多重尖峰同位素稀释分析在分子质谱中的应用，以使用 GC(EI)MS 仪器对汞的形态分析为例。已经应用了一种使用同位素富集的汞同位素的双尖峰同位素稀释方法，用于测定鱼类参考材料中的无机汞 Hg(II)和甲基汞 (MeHg)。该方法基于同位素模式分解的应用，用于同时测定甲基汞和无机汞的降解校正浓度。质量同位素分馏被用于计算 Hg 物种的校正浓度以及物种降解反应的程度，而不是同位素比。这里开发的同位素模式分解方程允许从 GC(EI)MS 质量同位素分馏模式直接计算不同的摩尔分数，并考虑到所用尖峰溶液中可能存在的杂质。该程序已成功用于分析两种不同的认证参考材料（BCR-464 和 DOLT-4），并与通过 GC(ICP)MS 获得的结果进行比较。对于金枪鱼（BCR-464）基质，在 70°C 下优化的开放聚焦微波提取 8 分钟的条件下，没有观察到相互转化反应。然而，在相同条件下，在认证的狗鱼肝脏 DOLT-4 中发现了明显的脱甲基化。通过 GC(ICP)MS 确认了甲基化和脱甲基化因子。转化反应取决于样品基质和所用衍生试剂。因此，不可能推荐适用于所有类型基质的最佳提取条件，这表明需要应用多种尖峰方法来测定生物样品中的 MeHg 和 Hg(II)。这里提出了使用广泛的 GC(EI)MS 仪器进行双尖峰同位素稀释分析方法，用于鱼类样品中无机汞和甲基汞的常规分析。对于两种汞物种，估计的方法检测限均低于 10 ng g(-1)。对于浓度在 0.1 至 5 µg g(-1) 之间的认证参考材料（CRMs）进行了精密度评估，获得的变异系数值在 7%至 2%之间。在分析的两个 CRM 中获得的浓度与认证值非常吻合，证明了该方法在这些浓度水平下的准确性。
