Raman spectroscopy: A tool for the quantitative analysis of mineral components of solid mixtures. The case of calcium oxalate monohydrate and hydroxyapatite

A quantitative analytical methodology based on Raman spectroscopy (RS) was developed for the compositional analysis of binary solid mixtures consisting of calcium oxalate monohydrate (COM) and hydroxyapatite (HAP). The ratios of the relative intensities of the Raman bands corresponding to HAP and COM were used for the construction of calibration curves used for the quantitative analysis. The intensities at 960 cm(-1), I-RHAP and 1462 cm(-1), I-RCOM, for HAP and COM, respectively, in the Raman spectra of each salt were used. A linear dependance was found for the ratio I-RHAP/I-RCOM on the inverse of the COM concentration (mole fraction) in the solid, binary mixtures. Comparison of this method with quantitative analysis of binary HAP-COM by powder X-ray diffraction (XRD), using the relative intensities of the 002 reflection of HAP and the 020 reflection of COM showed that although the limit of detection was comparable (approx. 1 mol%), RS analysis offered the relative advantage of performing analyses without the need of grinding the samples, thus making it possible for the analysis of layered deposits of the minerals investigated. (C) 1997 Elsevier Science B.V.