Quantification of immunoglobulin G and characterization of process related impurities using coupled protein A and size exclusion high performance liquid chromatography.

The present work describes two HPLC-UV methods for multi-protein quantification using (i) only a Protein A sensor cartridge (Protein A HPLC) and (ii) the same Protein A cartridge in combination with a size exclusion HPLC column (PSEC-HPLC). The possibility to simultaneously quantify immunoglobulin G (IgG) besides a non-binding protein such as bovine serum albumin (BSA) increases the applicability of Protein A HPLC. Its most pronounced feature is its independence of the buffer system, pH-value and salt content of the investigated sample solvent, which includes cell media. A comparison with the state-of-the-art, the photometrical Bradford method, shows that Protein A HPLC is as sensitive as Bradford, but that it comes with an extended linear range of 4 orders of magnitude, ranging from 0.15 [microg abs] to 1 [mg abs] absolute injected protein amount. The applicability of the PSEC-HPLC method is demonstrated for the analysis of real cell culture feed samples. While Protein A binds IgG, the SEC-column distributes the feed impurities by their molecular weight. The peak area ratios of IgG and the feed impurities of interest are then plotted against the collected sample fraction. These Protein A-Size-Exclusion-Chromatographic diagrams (PSEC-plot) combine the performance information of feed impurities and IgG in a single plot. Further it is shown that both methods are suitable for the performance evaluation of antibody purification media using static as well as dynamic binding experiments performed on DEAE-Fractogel and Capto Adhere. The investigated test samples were "mock" protein solutions with increasing complexity ranging from simple PBS buffer to serum free cell media and "real" cell culture feed solutions.