The results of a preliminary study on direct analysis of solid metals and nonconductive samples by inductively coupled plasma mass spectrometry (ICP-MS) are described. The aerosols ablated from solid samples by a ruby laser are introduced into an inductively coupled plasma, with detection of the resulting ions by a mass spectrometer. With conventional solution introduction, polyatomic species from mineral acids and solvents prevent the accurate determination of some trace analytes. However, using laser ablation, these background peaks are greatly reduced. The relative sensitivity factors for the laser ablation method are seen to vary from unity, with volatile elements such as Pb and Bi being more sensitive. Detection limits of rare-earth elements, Th and U in silicate rocks are excellent (0.02 -0.9 ppm at the effective integrating time of 1.4 s), being better than those of the examined elements in steel (1.7-29 ppm at the effective integrating time of 0.6 s).

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A laser ablation technique has been studied as a versatile method of direct solid sampling for subsequent elemental analysis. It has been successfully coupled with analytical techniques such as atomic absorption spectrometry (AAS)1-3, microwave-induced4, direct currents, and inductively coupled6,7 plasma atomic emission spectrometry (MIP-, DCP-and ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS).8-1° These tandem methods have a number of advantages such as high sensitivity, little or no sample preparation, small amount of samples required and the ability to analyze both conductive and nonconductive solids.We recently investigated laser ablation/ ICP-AES and ICP-MS in order to develop a rapid method for solid analysis. 7'8' 11,12 In these reports we showed that fractional vaporization, which limited analytical precision and accuracy, occurred during the ablation process. On the other hand, Hager10 indicated in a report on laser ablation/ ICP-MS that differences in the response factors were observed between free-running and Q-switched laser modes of operation • and that more uniform responses were obtained with the Q-switching mode. Thompson et a1.13 also showed that the matrix effect associated with an ablation event can be minimized with a maximum Q-switched laser. These results show that the magnitude of selective vaporization depends on the types of laser pulses.The present work aimed at investigating the laser dependence of selective vaporization. The use of six types of the laser pulses (three types of lasers each at two different running modes) was compared by collecting ablated particles, followed by analyzing them with solution-based ICP-AES or ICP-MS. Experimental Apparatus and operating conditionsThe operating conditions of the three types of lasers are shown in Table 1, together with the amounts of ablated

Direct analysis of silicate samples for the rare earth elements (REEs) by inductively coupled plasma mass spectrometry (ICP-MS) has been performed. Each finely ground sample (particle size <3 µm) was dispersed in 0.1% aqueous Triton X-100 solution and nebulized into an inductively coupled plasma. The resulting ions were detected by mass spectrometry. Parameters such as particle size, slurry concentration and argon carrier flow rate exercised a great influence on sensitivity, precision and accuracy of slurry nebulization/ICP-MS. Calibration curves were constructed using aqueous standard solutions. The extended dynamic range (EDR) detection system allowed the use of matrix element as an internal standard; this procedure was effective to correct the differences in sensitivity between the solution and the slurry methods. The optimum procedure was applied to the determination of REEs in standard silicate rocks of the Geological Survey of Japan. The precision ranged from 0.8 to 6.3 (RSD, %) for REEs contents of 0.13 -38 ppm. Detection limits of REEs were excellent (0.002 -0.02 ppm at the effective integrating time of 10 s). KeywordsSlurry nebulization, inductively elements coupled plasma mass spectrometry, silicate analysis, rare earthInductively coupled plasma (ICP) is now becoming accepted as an effective ionization source for subsequent mass spectrometric measurement. Comprehensive reviews have been presented by Date', Houk2 and Kawaguchi.3 In initial works on ICP mass spectrometry (ICP-MS), samples were generally introduced into ICP as aerosols of aqueous solutions; therefore, the dissolution of solid samples was required for many applications. This process is quite labor-intensive and time-consuming, especially for the analysis of refractory ceramic or silicate rocks.

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