QUANTITATIVE REE ANALYSIS OF SILICATES BY SIMS - CONVENTIONAL ENERGY FILTERING VS SPECIMEN ISOLATION MODE

REE relative ion yields obtained by secondary ion mass spectrometry (SIMS) from amphiboles and clinopyroxene samples are reported for both the conventional energy filtering (CEF) and specimen isolation (SI) modes of operation. Both techniques are equally quantitative, with particular advantages for each. Data obtained by SI are virtually free of molecular ion interferences, but the primary beam diameter is large (70-100 mum) and a slight loss of accuracy may occur due to critical beam placement within the unique geometry of the sample holder. Molecular ions of light REEs overlap peaks of heavy REEs in CEF operation, requiring a correction procedure involving determination of MO+/M+ yields and solution of simultaneous equations. The primary beam diameter, however, is approximately one quarter that for SI-an essential requirement for the analysis of small and chemically zoned crystals. Ion yields from crystals do not differ from those for glass of identical composition in CEF, but in SI are approximately 15 per cent lower.