Total reflection X-ray fluorescence analysis of high purity quartz: A bottom-up approach of uncertainty evaluation

Abstract

High purity quartz was analyzed using Total Reflection X-Ray Fluorescence (TXRF) spectrometry, during our participation in proficiency testing programme. The sample was digested in HF-HNO3 medium and the silica matrix was removed as silicon tetra fluoride by evaporation and repeated treatments with HNO3. Trace metallic impurities viz. K, Ca, Ti and Fe were quantified via the internal standard (using Ga) method in TXRF spectrometry. The z-score, zeta score and quality control sample analysis revealed the accuracy of the present determinations for all the analytes. Combined uncertainty for the measurement was evaluated through the bottom-up approach. Relative sensitivity of the TXRF spectrometer for the analyte with respect to the internal standard was found to hold the highest share of uncertainty. Detection limits for both the process blank and sample solutions were compared. Detection limits in the sample solutions were 1.86, 0.95, 0.94 and 0.30 mg kg−1 for K, Ca, Ti and Fe respectively. These studies brought out the importance of appropriate concentration of standard solutions for calibration and sensitivity measurements of the spectrometer, in addition to the quality of reference standard solution, for ensuring accuracy of the results.