Determination of Sr to Ca ratio in solid carbonate, fluoride, and nitrate samples using the fundamental parameters of EDXRF: experimental and empirical evaluation of non-destructive assays in light matrices

Abstract

Various aspects of the intensity ratio method of EDXRF, as applied to binary carbonate mixtures of Sr and Ca, are illustrated. To account for fluctuation during measurements, the intensity ratios of the characteristic X-rays have either been normalized or compared with the ratios of Compton and Rayleigh scattered primary X-rays. The effects of various instrumental parameters on all the measurables have been carefully investigated and utilized to assess the quality of the results obtained via the standardless, non-destructive EDXRF method for quantitative analysis. An empirical constant has been derived to relate the measured intensity ratios of Sr and Ca to their concentration ratios. The empirical relation involves only one additional factor—the Rayleigh to Compton peak ratio. The empirical constant entails three types of contributors: (i) the theoretical factors governing the X-fluorescence, which include the absorption jump factors, fluorescence yields, and branching ratios; (ii) the specific features of the measurement set-up, including the X-ray source energy, flux, relative attenuation of the characteristic X-rays in the sample chamber, and efficiency of the detector for the analytes; and (iii) the sample-composition-dependent variables, known as the effective mass attenuation coefficients, of the analyte and specimen for both the source and characteristic X-rays. Provided that the measurement conditions are followed, by simply feeding four input parameters, i.e., net counts for the Sr, Ca, Rayleigh and Compton peak, in the empirical equation, one can easily obtain the relative concentration of the two elements in various light matrices. The developed methodology has been applied to synthetic powder mixtures of two analytes in a variety of transparent matrices, including carbonate, nitrate and fluoride. Further, the concentration ratios of Sr and Ca in both solid powder and aqueous samples were determined. The analytical figures of merit of the present method, such as accuracy, precision and detection limits, were evaluated and qualified by comparison with reported values in the literature for similar analyses.