The equations for the coulometric efficiency η and steady state current I s (A) for the end-column amperometric detector in capillary zone electrophoresis have been investigated; they can be expressed as follows: η = 1 - m 1 exp(-m 2 DAUb) and I s = nFcU[1 - m 1 exp(-m 2 DAUb)] where D (cm 2 s - 1 ) is the diffusion coefficient of the species detected, A (cm 2 ) is the area of the electrode, U (cm 3 s - 1 ) is the mean volumetric velocity, b (cm) is the distance between the electrode and the capillary outlet, c (mol cm - 3 ) is the concentration of the species detected in solution, and n and F have their normal significance. m 1 and m 2 are constants which can be determined by experiment.The two equations have been verified experimentally.