High-precision determination of Mg/Ca and Sr/Ca ratios in carbonates by cool plasma quadrupole ICPMS
Date Issued
2004
Date
2004
Author(s)
Chiu, Han-I
DOI
zh-TW
Abstract
We have developed a high-precision analytical technique using quadrupole inductively coupled plasma mass spectrometry (Q-ICPMS, Agilent 7500s) for simultaneously measuring Mg/Ca and Sr/Ca ratios in carbonates, which are broadly used as environmental and climatic proxies in the Earth Sciences. Cool plasma technique with 650-W RF power was employed to diminish spectral interference. A desolvation introduction system with a micro-nebulizer was used to enhance sensitivity, improve detection limit and reduce sample size. Intensities of isotopes, including 24Mg, 43Ca and 86Sr, were all detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were calculated directly from intensity ratios, 24Mg/43Ca and 86Sr/43Ca, using external matrix-matched standards to correct for instrumental mass discrimination and low-frequency ratio drift. For Mg/Ca analysis, matrix effect of Ca level is 0.018 Mg/Ca (mmol/mol) / [Ca] (ppm). This problem can be overcome by holding [Ca] from 6-8 ppm in sample solution or correcting measured ratio with an empirical formula. Different Sr/Ca also slightly affects Mg/Ca determination with a slope of 0.017 Mg/Ca (mmol/mol) / Sr/Ca (mmol/mol). It is mainly caused by the formation of doubly-charge ion of 86Sr, which biases intensity measurement of 43Ca+ ion beam. This effect brings about only a trivial offset less than 1
Subjects
感應耦合電漿質譜術
鍶鈣比
鎂鈣比
ICP-MS
Mg/Ca
Sr/Ca
Type
thesis
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