ICP質量分析法による微量元素定量分析

抄録

Recent advances in inductively coupled plasma source-mass spectrometry (ICP-MS) has enabled us to determine trace and ultra-trace elements contained in various geochemical samples. Due to the high sensitivity and rapid mass scanning features of ICP-MS, multiple element analysis for trace elements can be performed without any pre-concentration procedure. The high sensitivity also permits direct spot analysis of solid geochemicl samples using laser ablation (LA) or laser probe (LP) sampling techniques. Spatial resolution as fine as 5-15μm has been achieved in the LP system. However, despite the great analytical ability of ICP-MS, some care should be taken in quantitative analyses. Spectroscopic interferences such as oxide molecular ions (MO⁺), doubly charged ions (M⁺⁺), and polyatomic ions (i. e., ArX⁺) affect the accuracy of measurements for the certain elements.Non-spectroscopic interferences, known as the matrix effect, also affect the analytical accuracy. There are two causes of the matrix effect: one originates in the plasma equilibrium and the other is the mass discrimination effect in an ion beam known as the "space charge effect". Differences in both the major chemical composition and introduction volume of analyte shift the aspect of the matrix effect. In order to attain high precision and accuracy in the analysis, optimization of the facility setting and analytical procedure is required to minimize those interferences. The problem in LA analysis is elemental fractionation mainly due to thermal heating of the sampling site during the laser ablation. This paper presents the facilities, functions, and analytical techniques of ICP-MS. Actual examples of terrestrial water analysis, rock analysis using solution samples, and micro analysis of minerals and bulk-rock analysis using LA-ICP-MS are also presented in this paper.