The thermogravimetric analysis of renal stones (in clinical practice).

Thermogravimetric (TG) analysis has been used as a routine technique for renal tract stone analysis. The results obtained in a consecutive series of 502 renal stones are described and evaluated. The technique is easy, rapid and gives quantitative information about stone composition. Results were compared with quantitative data obtained by standard chemical methods. Correlation coefficients for oxalate and urate were o-947 and 0-97 respectively. The comparison also showed that 63% of the stones could have been correctly analysed by TG analysis alone; in an additional 31%, TG analysis provided helpful information. TG analysis permits the identification of the proportions of mono- and dihydrate of oxalate present in calcium oxalate. It is confirmed that the centres of calcium oxalate calculi are richer in dihydrate than the exterior surfaces.