Speciation 98: Abstracts

Urolithiasis, i.e. the formation of kidney or bladder stones, constitutes a serious health problem, given that between 4 and 14% of the population, depending on geographic location, suffer from this condition. Approximately 70% of these stones have calcium oxalate as a major component but up to 26% are formed predominantly of calcium and/or magnesium phosphates. Uric acid is a less frequent constituent, cystine is observed in only about 1% of all cases and xanthine is the most infrequent constituent of urinary calculi.

Although a large number of factors may determine whether stone disease will occur, physicochemical aspects in general, solubility and crystallisation in particular, have been discussed recently. For the calculation of urinary saturation, the usefulness of modelling the ionic equilibria in urine by computer simulations has been clearly demonstrated. These models calculate the speciation in the aqueous phase by using the stability constants of the various complex species formed in urine as well as the solubility constants of the stone-forming solid phases. Therefore it is important to obtain proper information about these constants.

The general aim of this lecture is to give an overview of solubility determinations on some stone-forming and related compounds. The reliability of the literature solubility constants and those determined in our laboratory is assessed by comparing the results of computer simulations with the reported solubility data. Probably the largest ever, in terms of the number of reactions, species and thermodynamic quantities considered, equilibrium speciation model for solubility simulations of stone-forming solids in urine is presented. The model calculations permit the accurate prediction of previously reported solubility measurements carried out in various salt solutions and urine-like liquors.

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