Abstract: An improved capillary electrophoretic (CE) separation and indirect ultraviolet (in-UV) detection system was proposed for the amino acid analysis in tea samples with a homemade partition cell and a background electrolyte (BGE) of p-aminobenzoic acid (PAB). PAB improved the separation efficiency and detection limits of the amino acids. The partition cell prevented PAB from chemical reaction at the electrode, reduced baseline noise and kept electric current inside the cell. The separation parameters of the amino acids, such as different BGEs, BGE concentration, buffer pH and electroosmotic flow (EOF) modifiers, were investigated. The CE separation was carried out with the running buffer solution of pH 11.2, 10 mmol/L PAB containing 0.014 mmol/L cetyltrimethylamonium bromide (CTAB), an applied voltage of -15 kV and a detection wavelength of 254 nm. Sixteen amino acids were separated within 14 min under the selected conditions. The linear ranges of the amino acids were 0.02-0.60 mmol/L except for theanine (0.02-3.80 mmol/L) and γ-aminobutyric acid (0.02-2.00 mmol/L). The recoveries were in the range from 83.0% to 106%. The relative standard deviations of peak area were less than 5% (n=5) and the detection limits were in the range of 1.7-4.5 μmol/L. The method is fast, convenient and sensitive, and has been applied to the determination of 11 amino acids in tea samples satisfactorily.

Key words: amino acids, indirect ultraviolet detection, partition cell, tea , capillary electrophoresis (CE)