The crystallization and dissolution of sodium urate

The kinetics of dissolution and crystallization of monosodium urate monohydrate have been studied at 37°C using a highly reproducible seeding technique involving a specific sodium ion electrode. The relatively rapid rate of dissolution is proportional to the degree of undersaturation and appears to be controlled by the diffusion of electrolyte through a hydrodynamic layer at the crystal surface. The rate of growth, however, follows the square of the relative supersaturation and the evidence points to a surface-controlled process. The electrophoretic mobility of sodium urate crystals has also been measured in the presence of additives such as an organic phosphonate and sodium heparin. The influence of these substances upon the rate of crystallization of the negatively charged sodium urate is negligible. In contrast, methylene blue, a cationic dye, reduces the rate of reaction at moderately high levels (13 ppm).