Abstract:A general direct method to separate and quantify simultaneously 15 amino acids and 2 peptides was established by capillary electrophoresis(CE). This method had a wide linear range, low relative standard deviation, high precision and perfect reproducibility. The following optimized apparatus condition was explored. A fused-silica capillary 60 cm(50 cm to detector)×50 μm i.d. was used; working voltage of +25 kV was applied; background electrolyte was prepared of phosphate(50 mmol/L, pH 12.42) buffer with addition of methanol;and hydrodynamic injection of a sample (0.5 psi) during 5 sec was used at 25 ℃ with direct UV detection by diode array detector(DAD) at 206 nm. Quantitative analysis of a mixture of amino acids and peptides in maize seedlings can be achieved perfectly in this condition.