QUANTIFICATION OF LITHIUM, BERYLLIUM, AND BORON IN SILICATES BY SECONDARY-ION MASS-SPECTROMETRY USING CONVENTIONAL ENERGY-FILTERING

A SIMS procedure for Li, Be, and B quantification in silicates has bee n developed using the empirical approach of working curves via calibra tion with standards. Medium- to high-energy secondary ions have been u sed to reduce matrix effects affecting especially Li/Si ionization and to improve measurement reproducibility with respect to low-energy ion analysis for Li, Be, and B. In the case of Be, there has been evidenc e for a possible reduction of matrix effects, whereas in the case of B , matrix effects have been evidenced to be rather low at any ion energ y, and in such a case, the application of a voltage offset has been us eful only to improve measurement reproducibility. Positive ions of the isotopes Li-7, Be-9, B-11, and Si-30 (assumed as the matrix reference isotope), having emission kinetic energies ranging from approximately 75 to 125 eV, have been monitored using an ion microprobe Cameca IMS 4F. The calibration curves hold over extended concentration ranges fro m ppm to percent level by weight for light elements and silica content s ranging from a few percent to more than 80% by weight. Precision and accuracy of the method are generally estimated as better than +/-20% relative at the ppm level and better than +/-10% relative for element abundances of tens of ppm for Be and B. As for Li, the whole uncertain ty in the proposed SIMS procedure is evaluated at about +/-20% (28% fo r lead crystal glasses). These results have important implications for more extensive applications of SIMS as a 'routine'' microanalytical a nd bulk technique for the quantification of Li, Be, and B in silicate minerals and rocks.