Simultaneous determination of total homocysteine, cysteine and methionine in hypothyroid patients' plasma by liquid chromatography using platinum/poly(methyl violet) modified electrode

The fabrication and application of a novel electrochemical detection (ED) system with the platinum/poly(methyl violet) (Pt/MV) chemically modified electrode (CME) for high performance liquid chromatography (HPLC) were described. The Pt particles deposited on the poly-MV film were characterized by atomic force microscope (AFM). It was found that the Pt/MV CME exhibited efficiently electrocatalytic effect on the current responses of cysteine (Cys), homocysteine (Hcy) and methionine (Met) with relatively high sensitivity, stability and long-life of activity. In HPLC-ED, these three amino acids had good and stable current responses at the CME and their linear ranges were over three orders of magnitude (R ≥ 0.9996) with the detection limits being 7.5 × 10^-8 mol L^-1 for Cys, 1.0 × 10^-7 mol L^-1 for Hcy, 5.0 × 10^-7 mol L^-1 for Met. The application of this method coupled with microdialysis sampling for the determination of Cys, Hcy and Met in plasma from patients with hypothyroidism was satisfactory.