Estimation by infrared spectrophotometer of the calcium oxalate dihydrate to calcium oxalate monohydrate ratio.

According to the theoretical expression for calibration curve as a function of the optical absorption ratio of two peaks and with the analysis of the infrared spectra of the mixture samples of commercial calcium oxalate monohydrate and synthesized calcium oxalate dihydrate, the following quadratic equation was obtained; Y = 1.79 X2 - 30.90 X + 107.04 in which Y is the percentage of the purity of calcium oxalate dihydrate and X is the ratio of the relative optical absorption at 660 cm.-1 (the wave number at a characteristic absorption peak of calcium oxalate monohydrate) to that at 610 cm.-1 (that of calcium oxalate dihydrate) by regarding the line as a base-line that links the absorption valley at around 700 cm.-1 with that at 550 cm.-1 The linear correlation coefficient of the actual purity to the estimated purity obtained from this formula of calcium oxalate dihydrate is 0.995. When this formula is applied to the results derived from the infrared spectra of the mixture samples of commercial calcium oxalate monohydrate and calcium oxalate dihydrate obtained from urinary stones in duplicate in each percentage, the linear correlation coefficient is 0.991. This estimation method by infrared spectrophotometer of the calcium oxalate dihydrate to calcium oxalate monohydrate ratio gave a very close correlation between actual and estimated purity of calcium oxalate dihydrate and seems useful in the study of calcium oxalate urolithiasis.