The dissolution mechanism in a system undergoing complexation: salicylamide in caffeine solution

Abstract

The dissolution rate of compressed salicylamide discs has been measured in water and in caffeine solutions of increasing concentration at 15, 25, 37 and 45° in an apparatus rotating at 48 rev min−1 or more. Dissolution rate profiles showed breaks indicative of a shift in the mechanism of dissolution from interfacial towards transport control. The shifts occurred at higher caffeine concentrations on increasing the agitation rate or temperature. The dependencies of dissolution rates on agitation rates typified the intermediate type of dissolution and Arrhenius plots indicated that interfacial and transport processes participated in salicylamide dissolution.

Estimation of Dissolution Rate of Salicylamide in Complexing Media Using a Theoretical Diffusion Model

“…At 25' and 48 rpm, the predicted and measured rates are virtually identical over the full concentration range. There is reasonable agreement also a t 37' and 90 rpm; the deviation of the first two points is the cause of the lower correlation coefficient, 0.962, of the experimental regression line; its source is apparently interfacial control of the dissolution process when the transport is largely of free salicylamide (25). There is evidence of a similar deviation of the initial point a t 25 and 48 rpm, but it is small.…”