Determination of free d-alanine in the human plasma by capillary electrophoresis with optical fiber light-emitting diode-induced fluorescence detection

A new analytical method for d-alanine (d-Ala) based on capillary electrophoretic separation and optical fiber light-emitting diode (LED)-induced fluorescence detection has been developed. Fluorescein isothiocyanate (FITC) was used for precolumn derivatization of amino acids. The separation and determination of the derivatives was performed using a novel laboratory-built CE system with optical fiber LED-induced fluorescence detector. Optimal separation was performed at 15 kV using a background electrolyte solution consisted of 25 mmol L−1 sodium borate (pH 9.5), 18 mmol L−1 β-CD and 15 mmol L−1 SDS. High sensitive detection was obtained by the optical fiber LED-induced fluorescence detection using a blue LED as the excitation source. The limits of detection (S/N = 3) for d-Ala was 8.0 × 10−9 mol L−1. A calibration curve ranging from 2.0 × 10−8 mol L−1 to 1.0 × 10−6 mol L−1 was shown to be linear. Using this method, the levels of d-Ala in human plasma from healthy donors were determined.