Abstract:

A method of capillary electrophoresis with indirect ultraviolet (UV) detection was developed for the separation and determination of nine amino acids such as lysine, tryptophan, glutamic acid, etc. The effects of sodium dihydrogen phosphates concentration, pH of buffer and sample injection type and time on the reproducibility and efficiency were investigated. The optimum injection time was 5 s at 5 kPa. The optimum electrophoretic conditions were as follow: 10 mmol/L sodium dihydrogen phosphates (pH 10.2) containing 0.5 mmol/L cetrimonium bromide, 20 mmol/L nicotinic acid and 10%(v/v) methanol as running buffer, applied voltage of-15 kV, detection wavelength of 220 nm. The base line separation of the nine amino acids was achieved successfully within 11 min. The lowest detection limit was 0.3 mg/L. All of the nine analytes showed good linearities within 1.0-1000 mg/L. The relative standard deviations of migration time and peak area were 0.64%-5.83%. The recoveries of the eight amino acids spiked in a real sample were between 60.00% and 118.37%. The method was applied in the determination of the amino acids in honey samples from different nectar plants and origins. Prolin, serine and aspartic acid were found in five honey samples, and tryptophan was only found in a litchi honey sample. This method can provide good reference to the evaluation of the quality and nectar origin of honey.

Key words: amino acids, capillary electrophoresis (CE), honey, indirect ultraviolet detection