DEVELOPMENT OF A FUED GLASS DISC XRF FACILITY AND COMPARISON WITH THE PRESSED POWDER PELLET TECHNIQUE AT INSTITUTO DE GEOCIENCIAS, SAO PAULO UNIVERSITY

An X-ray fluorescence pressed powder pellet technique (PPP) currently in use at the X-Ray facility of the Institute de Geociencias, Sao Paulo University (IG-USP) has been extended to include additional elements and complemented by a full major and trace element calibration by fused glass disc (FGD) X-ray fluorescence. A total of 38 major and trace elements are available (F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Y, Zr, Nb, Mo, Sn, Sb, Ba, Pb, Bi, La, Ce, Nd, Th and U) with variable detection limits, but generally below 10 ppm for trace elements. Loss-on-ignitions determined by weight difference and totals provide extremely good control on data quality. A full analysis, including background, matrix correction and all relevant corrections can be achieved automatically in less than 60 minutes. Virtually any sample matrix can be accommodated. The data support the view that the fused disc and powder pellet techniques are complementary and together provide a definitive, rigorous XRF analysis. However, both techniques require considerable attention to details, with the glass disc technique prone to losses of F and S and increase detection limits for certain elements. The powder pellet technique requires fine micronising and caution when dealing with the light elements Si and Al. Additionally, the paper presents a new, previously unpublished experimentally determined Alpha coefficients for all matrix-corrected elements, which are based on the lithium metaborate system and contrast with the Philips theoretical alpha coefficients.