Determination of thiocompounds by liquid chromatography with amperometric detection at a Nafion indium hexacyanoferrate film modified electrode

Polynuclear indium(III) hexacyanoferrate(II, III) thin films are electrodep osited on a glassy carbon (GC) electrode through potential cycling between 1.1 and 0.0 V vs. SCE in a fresh modification solution containing potassium , indium(III) and hexacyanoferrate(III) ions. During the negative scans, th e cationic In3+ species interact with the simultaneously generated anionic Fe(CN)(6)(4-) to yield a sparingly soluble mixed-valent coating on the elec trode. Coated with Nafion film, the chemically modified electrode (CME) sho ws a better stability. The CME shows a single set of reversible, well-defin ed peaksc significantly separated from the solution responses. The apparent surface coverage is found to be 6.3 x 10(-9) mol/cm(2). This CME exhibits an efficient catalytic activity towards the rapid oxidation of thiocompound s in cyclic voltammetry, Cysteine (Cys), glutathione (GSH), 6-thiopurine (6 -TP) and methimazole (MMI) have good and stable current responses at the CM E in liquid chromatography with electrochemical detection (LC-ECD). The lin ear ranges are over three orders of magnitude and the detection limits are 1.6 pmol for Cys, 20 pmol for GSH, 20 pmol for 6-TP and 1.6 pmol for MMI. T he method has been successfully applied to assess the purity of methimazole , the contents of cysteine in human urine and other thiocompounds in artifi cial urines. (C) 1999 Elsevier Science B.V. All rights reserved.