Use of a Disposable Modified Carbon Paste Electrode for Liquid Chromatography-amperometric Detection of Theophylline and Three Metabolites in Human Serum

摘要

Chemically modified electrodes, constructed by incorporating potassium hexachloroplatinate K_2PtCl_6 into the graphite power/paraffin oil matrix used to fabricate conventional carbon paste electrodes, were shown to catalyze the electrooxidation of purine compounds including theophylline, 3-methylxanthine, 1,3-dimethyluric acid and 1-methyluric acid; the modifier electrodes display electrocatalytic activity for the oxidation of purines at 170 mV (vs Ag/AgCl) when used as sensing electrodes in amperometric detection following liquid chromatography. The K_2PtCl_6 electrodes permitted detection of the purines at similar values of applied potential. The limit of detection (LOD) of theophylline, 1-MUA, 3-MXT and 1,3-DMUA were 1.1 ng mL~(-1), 3.2 ng mL~(-1), 1.0 ng mL~(-1) and 11 ng mL~(-1), respectively. The calibration graphs were linear for theophylline and metabolites over the range of concentration used (50-3200 ng mL~(-1)). Theophylline and its metabolites can easily be separated and analyzed in one run using electrochemical sensor chromatography with a methanol - phosphate buffer containing 20 mM di-potassium hydrogen phosphate (pH 5.50). Serum samples were collected after the oral administration of black tea from human volunteers. Quantitative data for the determination of a micromolar amount of theophylline and its metabolites in serum samples are in agreement with data obtained by HPLC-UV.