The dissolution rate of zinc pyrithione.

Synopsis A method of measuring and correlating the rate at which zinc pyrithione dissolves during a shampoo is described. The rise in zinc concentration of a solution in a stirred vessel following the introduction of a dose of zine pyrithione suspension was measured as a function of time using atomic absorption spectrophotometry. An analysis of the mass transfer processes occurring during the dissolution of a suspended solid in a stirred vessel was used to correlate the concentration-time measurements. The analysis allows a calculation of the characteristic solution time, the mass transfer coefficient and the diffusion coefficient for the system. In this way the effect of changing shampoo formulation can be systematically studied.