Problem in analyzing cystine stones using FTIR spectroscopy

Abstract

Cystine stones are produced by an inherited disorder of the transport of amino acid cystine that results in excess of cystine in the urine (cystinuria). Cystine calculi in urinary tract present a significant problem in patients. We have recorded that cystine calculi are very uncommon in our region. Cystine crystals are unusually identified in the urinary deposits. The problem of recognizing cystine by FTIR as a component in mixture of stones is significant. The problem is compounded by the similarity of wavelengths of cystine with that of whewellite and uric acid. The objective of this paper is to elucidate the problems of identifying cystine in stone analysis and identifying a solution to get over this deficiency. Out of 1,300 urinary stones analysed by ordinary wet chemical methods and infrared spectroscopy, 30 stone samples, which were reported to have cystine peaks in significant numbers, were selected. These samples were powdered, mixed with potassium bromide, pelletized and taken up for FTIR analysis. The wavelength patterns were scrutinized by comparing with the peaks obtained by the reference standards of cystine. Spectra were also obtained from pure cystine. Comparison of spectra with those of whewellite and uric acid was performed. Then the samples were taken for Scanning electron microscopy with elemental distribution analysis X-ray (SEM-EDAX). The samples were made conductive by gold sputtering and were fed into JEOL JSM 35 C SEM machine. Morphology was recorded by taking photographs. Further elemental distribution analysis (EDAX) was carried out to identify the elemental composition. Of the 30 samples taken up for FTIR analysis, all showed spectra identifiable with the reference peaks for cystine. However, when these peaks were compared with those of whewellite and uric acid, all the stone samples showed duplication of peaks for whewellite and uric acid and whewellite. The pure cystine spectra showed identifiable peaks are in the range of 3026, 1618.28, 1485, 846.75 cm(-1), etc. (from the standard spectrum of pure cystine). All the analysis findings were correlated with EDAX findings. On doing EDAX, we could separately find out the components present in a mixture. Three stones contained elemental pattern to fit with those of cystine. Even though it is difficult to find out the presence of cystine molecule in FTIR, it is possible to recognize it through EDAX and will be possible to confirm the presence of cystine in mixed urinary stones.