LASER-ABLATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY (LA-ICP-MS) - A RAPID TECHNIQUE FOR THE DIRECT, QUANTITATIVE-DETERMINATION OF MAJOR, TRACE AND RARE-EARTH ELEMENTS IN GEOLOGICAL SAMPLES

A Nd:YAG laser in fixed-Q (free running) mode coupled to an inductivel y coupled plasma mass spectrometer was used to directly analyse presse d powder pellets of seven well-characterised silicate rock reference m aterials (AGV-1, BIR-1, DNC-1, G-2, NIST 2704, SCo-1 and W-2). The mul tielement limits of detection (LOD) were in the range 0.05-13 mug g-1 but with a majority of values better than 0.1 ug g-1. Using a narrow r ange scan LOD for the rare-earth elements (REE's) were between 11-84 n g g-1. Relative responses for the major elements indicate that the che mistry and mineralogy of individual rock samples influence the ablatio n behaviour, and that samples with very similar chemical and mineralog ical compositions exhibit similar elemental responses. The accuracy of major-element determinations, for the materials studied, was generall y better than +/- 5% with a precision of 10% RSD. First-row transition elements, incompatible elements and, in particular, REE's displayed a high degree of accuracy, with precision of generally < 10% RSD. Provi ding that samples and standards are matched both in terms of bulk chem istry and mineralogical composition, fully quantitative determination of major and trace elements is possible. Laser ablation ICP-MS is ther efore not only a rapid alternative method of elemental determination, but is also particularly applicable for a number of elemental groups w hose quantitative determination may be complicated if it is necessary to dissolve samples prior to analysis.