Use of capillary electrophoresis to determine the dilute protein concentration in formulations containing interfering excipients

Excipients like human serum albumin (HSA) or surfactants are often added to prevent non-specific adsorption of proteins to surfaces. An enzyme-linked immunosorbent assay (ELISA) has been routinely used to quantify proteins wh en such excipients interfere with conventional biochemical assays, e.g., UV and HPLC, and make the accurate determination of low protein concentration s and purl ly difficult. Although the ELISA is a very sensitive assay, the results have large experimental errors contributed by the complicating natu re of the assay. In addition, ELISA does not provide information about the qualitative degradation profile of protein, e.g., aggregation, cleavage, an d deamidation. As an alternative to the ELISA, a novel capillary electropho resis (CE) method has been developed to determine both the purity and quant ity of infergen(R) (Interferon alfacon-1) formulated with interfering excip ients like HSA. Results obtained from the CE method were consistent with th e results from ELISA, but the CE assay provided more reproducible and preci se results. The optimized CE method was successfully applied to the formula tion development by determining the recovery of diluted Infergen(R) in vari ous formulations.