Electrophoretic mobility of five polypeptides using nine different capillary chemistries over the pH range of 3.5-6.5

The performances of nine commercially available capillary zone electrophoresis (CZE) capillaries were tested and compared. Five model polypeptides, ranging in size from a tetrapeptide (604 D) to beta-lactamase 1 (approximately 29,000 D), were run at 32 degrees C on each of the nine capillaries using 10-mM ionic strength buffers at pH 3.5, 5.0, and 6.5. These results were then used to evaluate each capillary's performance. Factors used to assess the performance included comparison of observed electrophoretic mobilities (mu) to predicted mu (Overbeek-Wiersema model, O-W model; see appendix); reproducibility and consistency of the electroosmotic (EO) flow marker or internal marker throughout testing; and peak shape, height, and signal-to-noise. Five of the nine capillaries were evaluated further for migration time (MT) reproducibility over 50 injections of a polypeptide. A direct correlation was observed between peak tailing and slower observed mu. Those capillaries that exhibited a greater amount of tailing also had observed mu that were slower than predicted by the O-W model. As expected for any model, other capillaries produced observed mu that were faster than those predicted.