Tanaka Yu-Ki, Mikuni-Takagaki Yuko, Hidaka Kouki, Wada-Takahashi Satoko, Kawamata Ryota, Hirata Takafumi
Graduate School and Faculty of Pharmaceutical Sciences, Chiba University.
Geochemical Research Center, The University of Tokyo.
Anal Sci. 2019 Jul 10;35(7):793-798. doi: 10.2116/analsci.18P440. Epub 2019 Apr 5.
Stable isotope compositions of calcium (Ca) provide useful information concerning metabolic alterations of Ca in human and animal bodies. For the measurements of Ca isotope ratio, great care must be taken for the mass spectrometric interferences on Ca isotopes (Ca, Ca, and Ca) from doubly charged strontium (Sr) ions (Sr, Sr, and Sr). To obtain reliable stable isotope data of Ca, we developed a new correction technique for the mass spectrometric interferences by Sr ions based on standard addition method. Addition of a small fraction of Sr onto a Ca solution shifts the measured Ca isotope ratios on a three-isotope diagram (i.e., δCa and δCa) along a mixing line defined by both the true Ca isotope ratio and the Sr isotope ratio. Therefore, the true Ca isotope ratio of a sample can be obtained as the crossover point of mass dependent fractionation line and the mixing line. With the present correction technique, precise and accurate isotope ratio measurements can be made on analyte solutions having a C/C ratio (concentration ratio) of 0.03, which is 6 times higher than the C/C ratio applicable to the conventional correction technique.
钙（Ca）的稳定同位素组成提供了有关人体和动物体内钙代谢变化的有用信息。对于钙同位素比值的测量，必须格外小心来自双电荷锶（Sr）离子（Sr、Sr和Sr）对钙同位素（Ca、Ca和Ca）的质谱干扰。为了获得可靠的钙稳定同位素数据，我们基于标准加入法开发了一种针对Sr离子质谱干扰的新校正技术。向钙溶液中加入一小部分Sr会使在三同位素图上（即δCa和δCa）测得的钙同位素比值沿着由真实钙同位素比值和锶同位素比值定义的混合线移动。因此，样品的真实钙同位素比值可作为质量依赖分馏线与混合线的交叉点获得。采用目前的校正技术，可以对C/C比（浓度比）为0.03的分析物溶液进行精确和准确的同位素比值测量，这比适用于传统校正技术的C/C比高6倍。
