RESUMO
OBJECTIVE: To develop an in vitro model system for the investigation of calcium oxalate urinary stones under conditions of spontaneous precipitation. MATERIALS AND METHODS: Using a calcium-ion selective electrode and automatic titrator, a test solution was kept supersaturated with calcium oxalate and the rate of crystallization measured. RESULTS: During the spontaneous precipitation at constant supersaturation at 37 degrees C, the induction times required for the precipitation of calcium oxalate monohydrate were inversely proportional to the supersaturation of the solution. No transient phases were identified and the interfacial energy determined from kinetic analysis was 28.4 mJ/m2. The rates of precipitation showed a first-order dependence on the degree of supersaturation and were in good agreement with those reported for the in vivo formation of calcium oxalate monohydrate stones. CONCLUSION: This experimental model system allows precise measurements of the kinetics of calcium oxalate monohydrate. From the dependence of the rates of precipitation on supersaturation, a mechanism controlled by surface diffusion is suggested.
