A CRITICAL-LOOK AT QUANTITATIVE LASER-ABLATION ICP-MS ANALYSIS OF NATURAL AND SYNTHETIC GLASSES

In this paper, we examine techniques and problems of quantitative lase r-ablation ICP-MS analysis for natural and synthetic glass samples and discuss internal standardization, use of calibration curves, and sing le-standard calibration. Internal standards are used to normalize raw intensities and ate generally a low-abundance isotope of a major eleme nt in the samples. For zoned minerals, internal standards are used tha t show small compositional variations. Calibration curves are necessar y to define the ICP-MS response over a range of concentrations and are constructed using a series of geochemical reference standards of simi lar composition to the unknown materials to be analyzed. A series of c alibration curves for mafic-ultramafic acid felsic glasses are present ed, which generally show linear behavior. However, Zr, Y, and Ce calib rations are nonlinear and exhibit higher relative intensities for thes e elements at higher concentrations, This nonlinearity may be the resu lt of (1) large ranges in concentrations or (2) matrix effects involvi ng iron and total trace-element content in the glasses. Calibrations u sing a single geochemical reference standard can be attempted only if the calibration curves are linear and pass through the origin, and if the reference standard and the samples have similar compositions.