Direct and Accelerated Characterization of Formulation Stability

Formulation of products as well as process and quality control is in need of fast and efficient measurement techniques of the state of dispersion products. We review the basics of experimental techniques of stability assessment of suspensions and emulsions, procedures of accelerated stability testing, and discuss the relationship between results of "accelerated'' tests and the outcome under normal conditions of storage and usage (shelf life). Experimental results of the accelerated formulation testing are given with the focus on optical methods measuring stability based on space and time resolved changes of the volume concentration within the entire sample (STEP-Technology). In particular, acceleration of stability assessment acceleration by inclination and analytical centrifugation is demonstrated for diverse types of formulations. If the rate limiting step of destabilization is not sedimentation or creaming a combination with other established aging tests (temperature storage, freeze-thaw-cycles, physicochemical conditions, etc.) is suggested to reduce evaluation time.