Determination of Theophylline in Drugs and Tea on Nanosized Cobalt Phthalocyanine Particles Modified Carbon Paste Electrode

Abstract Metallophthalocyanine (MPc) and its derivatives are well known as electrocatalysts to catalyze oxidation or reduction of some species, such as cysteine, nitric oxide. Their nanosized particles may display the potential optics, electronic, catalytic, and structural properties. In this paper, carbon paste electrodes (CPE) modified with nanosized cobalt phthalocyanine (Nano‐CoPc) particles (Nano‐CoPc‐CPE) are fabricated. The electrocatalytic oxidation of theophylline (THP) on the Nano‐CoPc‐CPE is investigated by means of differential pulse voltammetry. The Nano‐CoPc particles perform better electrocatalytic activity to THP, the response current enhanced about 3.4 times compared to bulk CoPc‐modified CPE (B‐CoPC‐CPE). On optimal conditions, there is a good linear relationship between anodic peak current and THP concentration in the range of 4.0 × 10−7–1.0 × 10−4 mol L−1 with the detection limit of 1.4 × 10−7 mol L−1 (S/N = 3). The current responses of successive 40 measurements at the identical surface and at the renewed ones of Nano‐CoPc‐CPE are examined with relative standard deviation of 2.1% and 3.5%, respectively. It indicates that the electrode shows a good stability and reproducibility. It can be used to determine THP in tea and drug without separation from the matrix. The possible electrocatalytic mechanism is investigated by means of electrochemical method and UV/VIS spectroscopy.