Precise Determination of Element/Calcium Ratios in Calcareous Samples Using Sector Field Inductively Coupled Plasma Mass Spectrometry

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• 作者：Yair Rosenthal ; M. Paul Field ; and Robert M. Sherrell
• 刊名：Analytical Chemistry
• 出版年：1999
• 出版时间：August 1, 1999
• 年：1999
• 卷：71
• 期：15
• 页码：3248 - 3253
• 全文大小：78K
• 年卷期：v.71,no.15(August 1, 1999)
• ISSN：1520-6882

文摘

A new method was developed for rapid and precisesimultaneous determination of Mg/Ca, Sr/Ca, Mn/Ca,Cd/Ca, Ba/Ca and U/Ca ratios in foraminiferal shellsusing sector field inductively coupled plasma mass spectrometry (ICPMS). Element/calcium ratios were determined directly from intensity ratios using external, matrix-matched standard to correct for instrumental massdiscrimination. Because of large differences in the abundance of chemical constituents of the foraminiferal shell,major elemental ratios were determined in analog mode(using ²⁴Mg, ⁴³Ca, ⁴⁴Ca, ⁵⁵Mn, and ⁸⁸Sr) whereas traceelemental ratios were determined in pulse-counting mode(using ¹¹¹Cd, ¹³⁸Ba, ²³⁸U, and the low-abundance ⁴⁶Caisotope). Matrix-induced variations in mass discrimination over a calcium concentration range of 2.0-24.5 mMwere observed only for Mg/Ca and Cd/Ca ratios. However,these effects are negligible if the samples and standardcalcium concentration are within a factor of 2-3. Multiratio method reproducibility was better than previouslyreported for other ICPMS methods yielding precision (1mages/gifchars/sigma.gif" BORDER=0 >)of Sr/Ca = 0.45%; Mg/Ca = 0.45%, Mn/Ca = 0.8%, Cd/Ca = 1.7%, Ba/Ca = 0.7%, and U/Ca = 1.4% forforaminifera samples as small as 25 mages/entities/mgr.gif">g. Using thisapproach for a single-ratio analysis, Sr/Ca ratios weredetermined with precision of 0.06% (1mages/gifchars/sigma.gif" BORDER=0 >) on carbonatesamples as small as a single foraminifera shell (<10 mages/entities/mgr.gif">g).The new method is more sensitive, more precise, andsimpler to use than previously available ICPMS techniques. It provides an efficient tool for simultaneousdetermination of several elemental ratios of paleoceanographic interest in a single foraminiferal sample, therebyreducing overall sample size requirement and analysistime.