Qualitative and quantitative analysis of urolithiasis with the Rietveld method (x-ray diffraction)

Background. The Rietveld method is one of the most innovative and most important applications in x-ray diffraction and has now, for the first time, been applied to standard-free precise quantitative crystallographic analysis of urinary stones. Material and methods. The capability of the Rietveld method was demonstrated by analysis of a synthetic mixture of five typical urinary stones: whewellite, hydroxylapatite, brushite, struvite, and uric acid, with 20 weight % for each pure component. Results. The quantitative phase analysis ( Rietveld method) yielded a mean absolute error of only 1.6% for the weight fractions of the single urinary stone components. The largest error in weight fraction, 2.3%, occurred with hydroxylapatite, caused by the typical insufficient crystallinity. Conclusion. Crystallographic analysis of complex urinary stones with the aid of x-ray diffraction, in combination with a Rietveld structure refinement, is the method of first choice for qualitative and quantitative phase analysis. With this tool, significant changes in weight fractions for recurrent urinary stones can be precisely detected, with therapeutic consequences.