High precision isotope ratio measurements of mercury isotopes in cinnabar ores using multi-collector inductively coupled plasma mass spectrometry
High precision isotope ratio measurements of mercury isotopes in cinnabar ores using multi-collector inductively coupled plasma mass spectrometry
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作者：
Hintelmann, H;Lu, SY
采用多收集器电感耦合质谱法（MC-ICP- MS）对不同国家朱砂矿石中汞同位素比值进行了高精度测定。相对于NIST SRM 1641d汞溶液，δ(198/202)汞的值在0.0 - 1.3‰之间变化。δ值的典型外部不确定度为0.06至0.26‰。汞经硼氢化钠还原后以单质汞的形式进入血浆。在同时生成氢化铅的过程中，铅同位素发生了明显的分馏，这使得使用测量的（208/206）Pb比无法将汞同位素比例归一化。采用同时测量的（205/203）Tl比值来校正Hg比值。使用10 ng ml(-1) Hg溶液，采样10分钟，引入60 ng Hg，同位素比值测量的内部精度低至14 ppm。绝对汞比偏离代表性的IUPAC值约0.2% / u。这一观察结果是由于MC-ICP- MS测量中指数律的不足来纠正质量偏差。由于缺乏精确表征的汞同位素比率标准，我们无法明确确定矿石样品的绝对汞比率，这突出了对认证标准材料的迫切需要。
Variations in Hg isotope ratios in cinnabar ores obtained from different countries were detected by high precision isotope ratio measurements using multi-collector inductively coupled mass spectrometry (MC-ICP- MS). Values of delta(198/202)Hg varied from 0.0 - 1.3parts per thousand relative to a NIST SRM 1641d Hg solution. The typical external uncertainty of the delta values was 0.06 to 0.26parts per thousand. Hg was introduced into the plasma as elemental Hg after reduction by sodium borohydride. A significant fractionation of lead isotopes was observed during the simultaneous generation of lead hydride, preventing normalization of the Hg isotope ratios using the measured (208/206)Pb ratio. Hg ratios were instead corrected employing the simultaneously measured (205/203)Tl ratio. Using a 10 ng ml(-1) Hg solution and 10 min of sampling, introducing 60 ng of Hg, the internal precision of the isotope ratio measurements was as low as 14 ppm. Absolute Hg ratios deviated from the representative IUPAC values by approximately 0.2% per u. This observation is explained by the inadequacy of the exponential law to correct for mass bias in MC-ICP- MS measurements. In the absence of a precisely characterized Hg isotope ratio standard, we were not able to determine unambiguously the absolute Hg ratios of the ore samples, highlighting the urgent need for certified standard materials.