Validation of the infrared spectroscopy method for analysis of the composition of urine concretes.

The aim of this study was to validate the method for analyzing the composition of calculus using infrared (IR) spectroscopy by studying model mixtures of salts. Study was made with an ALPHA-P IR Fourier spectrometer with OPUS software (Bruker, Germany). The samples of pure chemical salts manufactured by Sigma-Aldrich USA were used to validate the method. Salt mixtures were prepared in ratios of 10/90, 50/50 and 90/10. To assess the effect of the fraction size on the calculus component results, were used calculi of patients with urolithiasis. For each mixture were used 10 repeated measurements. Analysis of the composition of model salts showed that in the study of pure cystine salt CV(%) was 0,79%, calcium carbonate - 0,92%, sodium urate - 0,97%, calcium oxalate monohydrate - 4,94%, magnesium ammonium phosphate - 5,59%. And the most common components were analyzed in the composition of complex mixtures, including 90%, 50% and 10% of the investigated component. Calcium oxalate monohydrate has CV(%) 5.70% in mixture 9 part of it to one part of impurities, in mixture 50/50 - 21.57% and in 10/90 - 5.70%. For uric acid in 90/10 - 2.20%, in 50/50 - 10.09%, in 10/90 - 31.94%. For calcium carbonate in 90/10 - 9.02%, in 50/50 - 11.98%, in 10/90 - 24.70%. The dispersion analysis showed that the weighed portions of salts with a particle diameter of more than 0.8 mm provide reproducibility with a CV - 11.48%, with a diameter of 0.2-0.8 mm - 5.35%, and finally less than 0.1 mm - 2.28%. The accuracy of the method is high, but the reproducibility of the IR-spectroscopy method is relatively low in the analysis of stones of mixed composition, due to the greater error in the determination of impurities. Laboratories should pay special attention to optimizing sample preparation to ensure particle fineness less than 0.1 mm.