This chapter describes a CE-UV-MS method for the identification and quantification of insulin in pharmaceutical formulations in a single run. The CE conditions are optimized to avoid the adsorption of the protein onto the capillary wall. Particular attention is paid regarding the choice of the internal standard. A strategy based on multiple injections is applied to correct both ionization and injection variabilities. The methodoligy is validated according to internal guidelines and the obtained accuracy profile demonstrates the ability of the CE-UV-MS method to quantify insulin in pharmaceutical formulations within a 15% acceptance range. This strategy can be implemented in the field of quality control, as well as in the detection of counterfeits.