Determinazione di Zr e Y in peridotiti mediante fluorescenza a raggi X con il metodo delle aggiunte.

A “spiking method” in X-Ray Fluorescence (XRF) has been developed in order to analyze Zr and Y at very low concentration level in peridotitic rocks. The “spike” mixture is constituted by pure Zr element and Y oxide (Y2O3) diluted in a quartz powder (SiO2 > 99.9 %). For each sample, 4 different pressed pellets spiked with 0, 3.3, 6.7 and 10 ppm for Zr and 0, 5, 10, 15 ppm for Y, respectively, have been prepared. The correlations obtained between XRF intensities and spiked concentration are very good (R2 >= 0.97) and allows the actual Zr and Y concentration of each sample to be calculated. Precision and accuracy are believed to be <± 30% for Zr and < 20% for Y respectively. When the intensities of Zr and Y are plotted versus the concentrations of all the pressed pellets, good calibration curves in the range of 0¸15 ppm are obtained (uncertainties <±10%). The international standards available in this range of concentrations do not deviate appreciably from the regression lines, with the exception of NIM standards.