Chemically modified electrodes, constructed by incorporating potassium hexachloroplatinate K2PtCl6
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 K2PtCl6 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.