Scientific aspects of urolithiasis : quantitative stone analyses and crystallization experiments

Doctoral Thesis


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University of Cape Town

This thesis describes two aspects of the various scientific approaches to the study of urolithiasis. In the first instance, the theory, development and results of three quantitative analytical procedures are described while in the second, crystallization experiments in a rotary evaporator are presented. Of the different methods of quantitative X-ray powder diffraction analyses, the 'internal standard method' and a microanalytical technique were identified as being potentially the two most useful procedures for the quantitative analysis of urinary calculi. 'Reference intensity ratios' for 6 major stone phases were determined and were used in the analysis of 20 calculi by the 'internal standard method'. It is concluded that the attainment of accurate results using this procedure is not easily achieved because of problems such as the unavailability of standards which realistically mimic stone composition, sample preparation, overlap of reflections from sample components and standards and the requirement of 'infinitely thick' specimens ( > 250 mg). For the microanalytical technique, micro-quantities of 10 calculi from the original 20 were deposited on silver filters and were quantitatively analysed using both, the attenuation of the Ag peak and the separately measured absorption coefficients μ*· Inductively coupled plasma atomic emission spectroscopic (ICP-AES) methods were also investigated, developed and used in this study. Various procedures for the digestion of calculi were tested and a mixture of HNO₃ and HClO₄ was eventually found to be the most successful. The major elements Ca, Mg, and Pin 41 calculi were-determined. For the determination of trace elements, a new microwave-assisted digestion procedure was developed and used for the digestion of 100 calculi. Thereafter the major elements Ca, Mg and P together with the minor and trace elements Al, Cu, Fe, K, Li, Mn, Mo, Na, Pb, S, Sr and Zn in all 100 stones were simultaneously determined. The data so obtained were subjected to 3 types of statistical analyses involving direct correlations, scatter plots and a relatively new multivariate analysis of logarithmic data known as a 'covariance biplot'. Several interesting correlations were obtained. Fluoride concentrations in two stone collections - 20 calculi from India and 42 from South Africa - were determined using a fluoride-ion sensitive electrode and the HNO₃/HClO₄ digestion procedure used for the ICP study. Direct measurement of fluoride proved unsuccessful thereby necessitating the investigation and development of a diffusion technique. Using this method the fluoride content of both collections was determined. A series of crystallization experiments involving a standard reference artificial urine was carried out in a rotary evaporator. The effect of pH and urine composition was studied by varying the former and by including certain components (uric acid, urea, creatinine, MgO, methylene blue, chondroitin sulphate A, fluoride) in the reference solution. Crystals formed in these experiments were subjected to qualitative and semi-quantitative X-ray powder diffraction analyses. Scanning electron microscopy of several deposits was also carried out. Similar deposits to those observed in calculi were obtained with the fast evaporator. The results presented suggest that this system provides a simple, yet very useful means for studying the crystallization characteristics of urine solutions. The quantitative analytical procedures described in detail in this thesis can serve as model techniques for other workers involved in stone research. Together with other approaches such as the crystallization experiments discussed, these procedures can lead to a better understanding of the aetiological processes which govern stone formation.

Bibliography : pages 211-267.