An electrophoresis capillary that incorporates two enzymes for the simultaneous determination of glucose and l-glutamate is described. The enzymes deposited along the separation capillary walls react with their respective substrate as they are separated during the electrophoresis to produce hydrogen peroxide that is detected by amperometry as the hydrogen peroxide zone emerges from the end of the capillary. Even though both enzyme reactions produce a common product, hydrogen peroxide, the hydrogen peroxide produced by each enzyme reaction stays in narrow zones that migrate the length of the capillary at different rates. The rate of migration for the individual H2O2 zones is consistent with the expected mobility of neutral glucose and of anionic l-glutamate, respectively. This property allows each enzyme substrate to be characterized in a single experiment and in the presence of other electroactive substances.