Objectives: The analysis of urinary stones is used for the diagnosis of the etiology of an episode of nephrolithiasis. The technique considered as standard for this purpose is infrared spectroscopy (IR). However, when the urinary stone is formed by a mixture of components, only semi-quantitative information can be achieved using IR. The objective of this work is the development of a quantitative method.
Design and methods: Bands in the IR spectra of several mixtures were studied, in order to design a calibration model useful to determine the quantitative composition of the urinary stones. For mixtures of two components, four mathematical models were proposed. To assess the validity of these models, nine series of mixtures of two components were prepared, using the most frequently compounds found in urinary stones, for analyzing by ATR-FTIR spectroscopy (Attenuated Total Reflection Fourier Transformed Infrared).
Results: Nine series of nine mixtures of two components were prepared for this work. The IR spectrum was recorded for each mixture and the absorbance intensities at selected wave numbers were used to apply the proposed mathematical models. There were good linear correlations between the analytical signals (IR absorbances) and the analytical responses (weight fractions) using the calibration lines. The validity of the method was checked by the comparison between the weight fractions resulted from the calibration lines and the real weight fractions obtained by weighing, presenting good correlation parameters.
Conclusions: The method developed in this work has been useful for the quantification of compounds which are commonly found in urinary stones. This method allows a total characterization of the urinary stones (qualitative and quantitative) by means of IR spectroscopy.
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