Improvement of injection conditions for zone electrophoresis of proteins in capillaries coated with N, N-didodecyl-N, N-dimethylammonium bromide

Fused silica capillaries treated with N, N-didodecyl-N, N-dimethylammonium bromide was used in capillary electrophoresis to separate basic proteins using ammonium acetate as BGE at pH 4.0, 70 mM. This surfactant forms a semi-stable coating that provides a strong anodic electroosmosis; however, such coating must regularly be regenerated to maintain efficiency and reproducibility. The temporal stability of the coating was greatly improved by a new procedure as described in previously study by our group. In this study, it is found such experimental conditions that the starting zone could be enriched without loss of sample. The injection of a short plug of the BGE diluted 100 times for 3 sec in 50 µm i.d. capillaries behind the sample zone at 15 kV gave the best performance, whereas, a plug of lower dilution degree (10 times) in 25 µm i.d injected for 3 sec at the same field strength gave the optimum results for this dimension. In conclusion, those conditions were found to effectively decrease the loss of sample and to give a higher separation performance in regard to peak efficiency and resolution compared to injecting the sample without a plug.