Intrinsic dissolution of lithium carbonate in aqueous solutions

Intrinsic dissolution rate studies were carried out on lithium carbonate discs that were prepared with the disc in a component on the final support. This overcame the problem of further handling of the fragile discs. Dissolution media employed were similar to those used for the routine evaluation of lithium carbonate dosage forms. Linear dissolution rate profiles were found in simulated gastric fluid (SGF), Tris buffer and water. Data in SGF and water showed positive intercepts with the Levich model. The dissolution process of lithium carbonate was considered to be complex. Dissolution profiles in simulated intestinal fluid (SIF) containing phosphate showed a marked initial curvature and a subsequent reduced dissolution rate. This was due to the precipitation of trilithium phosphate onto the disc. Dissolution rate studies on lithium carbonate dosage forms could be invalidated where a phosphate buffer system has been used.