Trace analysis of d-tyrosine in biological samples by microchip electrophoresis with laser induced fluorescence detection

A rapid and sensitive microchip electrophoresis (MCE) method with laser induced fluorescence (LIF) detection has been developed for the quantification of d-tyrosine (Tyr) in biological samples. The assay was performed using a MCE-LIF system with glass/poly(dimethylsiloxane) (PDMS) hybrid microchip after pre-column derivatization of amino acids with fluorescein isothiocyanate (FITC). Chiral separation of the derivatives was achieved by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) using γ-CD as chiral selector in the running buffer. d/l-Tyr enantiomer was well separated in less than 140 s. The limit of detection (S/N = 3) was 3.3 × 10−8 M. Using the present method, d-Tyr level in human plasma was found to vary significantly from normal humans to patients suffering from renal failure.