Embodiments of the invention include polypeptide formulations and methods for making, using and characterizing them. Embodiment of the invention include stabilized polypeptide formulations, for example stable glucose oxidase formulations that can be used with glucose sensors used in the management of diabetes. Another embodiment of the invention includes methods to characterize the concentration of nonionic surfactants in stabilized polypeptide formulation for example stable insulin formulations that can be used in the treatment of diabetes.