Direct measurements on individual microcapsule dissolution as a tool for determination of release mechanism

A method is described for simultaneous microscopic observation of individual microcapsule core material dissolution together with quantitative measurement of the individual kinetics of release of the contents. These may be conductimetric in the case of ionized materials or spectrophotometric otherwise. This enables correlation of changes in core surface area during dissolution with kinetics. Surprisingly, both ethyl cellulose- and polymethacrylate-coated cores of potassium dichromate crystals, used as a model, showed localized internal dissolution universally, providing evidence of the exit of the salt via pores in the membrane, in spite of the kinetics being invariably zero order, as expected for individual microcapsules. The advantages of the method are presented.