Simultaneous separation of anionic and cationic proteins by capillary electrophoresis using high concentration of poly(diallyldimethylammonium chloride) as an additive

The simultaneous separation of anionic and cationic proteins has been achieved by addition of high concentration of poly(diallyldimethylammonium chloride) (PDDAC) in capillary electrophoresis. A capillary was filled with PDDAC so that it would act as ion-pair reagents in the separation of anionic proteins. On the other hand, the PDDAC can also be used as coating additives for the analysis of cationic proteins. Increasing the concentration of PDDAC in the separation buffer had the ability to improve the separation efficiency, change the electrophoretic mobility, and alter the separation selectivity; however, this was not true in the case of analyzing proteins by using the PDDAC larger than 1.6%. By both using a buffer containing 1.6% PDDAC and applying pH-stepwise techniques, 13 proteins with a wide range of pI (4.7–11.1) and molecular masses (6.5–198.0 kDa) could be separated within 30 min in a single run. In addition to this separation, we observed not only more peaks from α-chymotrypsinogen A and aprotinin but also the bovine serum albumin (BSA) dimer and trimer. With the 50 nL protein injection sample, the limits of detections at signal-to-noise of 3 for proteins are in the range of 0.07–0.79 μM. Except for BSA, the relative standard derivation values of migration time and peak height for all proteins were <1.3 and <6.9%, respectively. We suggested that this proposed method is a promising approach for clinical diagnosis and proteomics applications.