Rapid Determination of Free Amino Acids in Milk by Microchip Electrophoresis Coupled with Laser-induced Fluorescence Detection

A simple and sensitive method for determination of free amino acids in milk by microchip electrophoresis (MCE) coupled with laser-induced fluorescence (LIF) detection was developed. Seven kinds of standard amino acids were derivated with sulfoindocyanine succinimidyl ester (Cy5) and then perfectly measured by MCE-LIF within 150 s. The parameters of MCE separation were carefully investigated to obtain the optimal conditions: 100 mmol center dot L-1 sodium borate solution (pH 10.0) as running buffer solution, 0.8 kV as injection voltage, 2.2 kV as separation voltage etc. The linear range of the detection of amino acids was from 0.01 mu mol center dot L-1 to 1.0 mu mol center dot L-1 and the detection limit was as low as about 1.0 nmol center dot L-1. This MCE-LIF method was applied to the measurements of free amino acids in actual milk samples and satisfactory experimental results were achieved.