Liu Hou-Chun, Chung Chuan-Hsiung, You Chen-Feng, Chiang Yi-Hsuan
Department of Earth Sciences, National Cheng Kung University, 70101, Tainan, ROC, Taiwan.
Earth Dynamic System Research Center, National Cheng Kung University, 70101, Tainan, ROC, Taiwan.
Anal Bioanal Chem. 2016 Jan;408(2):387-97. doi: 10.1007/s00216-015-9070-y. Epub 2015 Oct 12.
A protocol for highly accurate and precise determination of Sr isotope ratios in plant materials, (87)Sr/(86)Sr and δ (88/86)Sr, by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is presented in this study. An Eichrom Sr resin was used for matrix separation and an improved Zr empirical external normalization coupled with standard-sample bracketing method (Zr EEN-SSB) was applied to mass bias correction during Sr isotope MC-ICP-MS measurements. Potential influences of matrix elements, and polyatomic and isobaric interferences on the Sr isotopic determination were further evaluated using NIST SRM 987 Sr isotopic standard spiked with various amount of Ca, Mg, and Rb contents. Concentrations of Ca and Mg lower than 30 ng g(-1) or Rb < 2 ng g(-1) in 150 ng g(-1) Sr analyte were estimated to have only a minor effect on Sr isotope ratios determination. On the other hand, intensity differences between sample and standards (IntSample/IntStandards) represented a large δ (88/86)Sr deviation of <0.9 or >1.3, reflecting the significance of intensity bias attributed to different mass bias behavior. An apple leaf material, NIST SRM 1515, was adopted as the plant material for overall evaluation of sample digestion, matrix separation, and potential spectral interferences on the measurements of Sr isotope ratios. Our results suggest that the partially remaining organic compounds in the incomplete digestion would have a significant bias on the extraction chromatography procedure, resulting in sizable uncertainty in δ (88/86)Sr ratios. Thus, complete digestion of the organic-enriched materials is of great importance for efficiency assurance in matrix separation. Extraction chromatography works well for the total digested samples, where Ca, Mg, and Rb were efficiently removed. The obtained average (87)Sr/(86)Sr and δ (88/86)Sr values for the NIST SRM 1515 apple leaves are 0.71398 ± 0.00004 and 0.23 ± 0.03‰ (2SD, n = 10), respectively.
本研究提出了一种通过多接收电感耦合等离子体质谱法（MC-ICP-MS）高精度、精确测定植物材料中锶同位素比值（87）Sr/（86）Sr和δ（88/86）Sr的方法。采用Eichrom Sr树脂进行基体分离，并在锶同位素MC-ICP-MS测量过程中应用改进的锆经验外部归一化结合标准-样品括号法（Zr EEN-SSB）进行质量偏倚校正。使用添加了不同含量的钙、镁和铷的NIST SRM 987锶同位素标准物质，进一步评估了基体元素以及多原子和同量异位素干扰对锶同位素测定的潜在影响。估计在150 ng g-1的锶分析物中，钙和镁的浓度低于30 ng g-1或铷<2 ng g-1对锶同位素比值测定的影响较小。另一方面，样品与标准物质之间的强度差异（IntSample/IntStandards）表示δ（88/86）Sr偏差较大，<0.9或>1.3，反映了归因于不同质量偏倚行为的强度偏差的重要性。采用苹果叶材料NIST SRM 1515作为植物材料，对样品消解、基体分离以及对锶同位素比值测量的潜在光谱干扰进行全面评估。我们的结果表明，不完全消解中部分残留的有机化合物会对萃取色谱过程产生显著偏差，导致δ（88/86）Sr比值存在相当大的不确定性。因此，完全消解富含有机物的材料对于确保基体分离效率至关重要。萃取色谱法对完全消解的样品效果良好，其中钙、镁和铷被有效去除。NIST SRM 1515苹果叶获得的平均（87）Sr/（86）Sr和δ（88/86）Sr值分别为0.71398±0.00004和0.23±0.03‰（2SD，n = 10）。
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