Use of Raman Spectroscopy for the Quantitative Analysis of Calcium Oxalate Hydrates: Application for the Analysis of Urinary Stones

Abstract

The potential use of the Raman spectroscopy (RS) for the quantitative analysis of the mineral components of urinary stones consisting mainly of the mono- and dihydrate salts of calcium oxalate has been demonstrated. The quantitative analysis was based on the construction of calibration curves made of known mixtures of synthetically prepared pure calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD). The Raman spectra of well-mixed powdered samples of COM and COD were recorded, and the characteristic bands at 1462 and 1477 cm⁻¹ for COM and COD, respectively, were used as the basis for the quantitative analysis. It was found that x_M = (I_R – 0.134)/(0.8I_R + 1.52), where x_M is the molar fraction of COM in the solid mixture and I_R represents the intensity ratio of the Raman band at 1462 cm⁻¹ to that of 1477 cm⁻¹. The calibration curve was used for the analysis of a typical urinary stone surgically removed, and it was found that x_M = 0.33. This finding was confirmed by infrared quantitative spectroscopic analysis. Quantitative analysis using the proposed Raman technique had a detection limit of approximately 0.6 mol % content in COM. The relative advantage of RS lies in its potential use as a nondestructive analytical technique for the mineral composition of urinary stones.