Voltage programming in capillary zone electrophoresis

Temperature is an important factor in capillary zone electrophoresis since it affects the viscosity and the pH of the buffer solution. In this study, a capillary tube with a large radius (130 μm I.D.) and filled with buffer at a high ionic strength is used to generate substantial joule heat within the capillary tube to force a significant increase in temperature, in turn to decrease the viscosity and to change the pH of the bufrer solution. From a study of the degree of dissociation of analytes at different voltages, we show that voltage-induced pH change is significant in 0.1 M tris(hydroxyamino)methane (THAM) but not in 0.025 M hydrogencarbonate buffer system. A step change in voltage from 15 to 25 kV is implemented to generate a pH gradient in the THAM buffer solution. The results show that the method is useful for separating phenols which cannot be separated at a fixed voltage.