Determination of theophylline in tea and drug formulation using a Nafion®/lead–ruthenium oxide pyrochlore chemically modified electrode

Square-wave voltammetry was used for the determination of trace amounts of theophylline in tea and drug formulation at a Nafion®/lead–ruthenium oxide pyrochlore chemically modified electrode. This chemically modified electrode exhibits a marked enhancement of the current response compared to a bare glassy carbon electrode. The calibration graph for the determination of theophylline was linear up to 100 μM in 0.1 M, pH 3 phosphate solution with a detection limit (S/N=3) of 0.1 μM. The results of 15 successive repetitive measurement-regeneration cycles showed a relative standard deviation of 1.3% for 10 μM theophylline indicating that the electrode renewal gives a good reproducible surface. Quantitative analysis was performed by the standard addition method for the theophylline content in commercially available tea and drug.