WO3 nanoparticles based electrochemical sensor for trace determination of theophylline by adsorptive stripping differential pulse voltammetry

Theophylline (1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione ) is a kind of methyl xanthine derivatives which exists widely in nature. It was used in treatment of infant apnea, asthma andchronic bronchospasm of adults [1]. The most accepted range of effective theophylline plasma concentration in adults is between 5 and 20 mg mL-1. Levels higher than 20 μg/mL can cause arrhythmia, fever, dehydration, insomnia, anorexia, coma, heartburn tachycardia and cardiacarrest. Because theophylline exists in many soft drinks, foodstuff and natural products, such as cocoa, tea and chocolate [2], it is important to develop a simple, accurate and rapid method for theophylline determination. The main reported procedure for the determination of theophyllinein different samples is chromatographic methods. In spite of the high sensitivities of the chromatographic methods, they are very expensive; involve the use of complex procedures with several sample manipulations, require long analysis time and trained personnel.In recent years, nanostructured metal oxides have been widely applied as sensing material in sensors and biosensors because of their high chemical stability, biocompatibility, structuralflexibility, higher catalytic behavior and strong adherence to substrates [3]. In the present work, an electrochemical sensor for theophylline determination was prepared by the modification of a glassy carbon electrode (GCE) with the nano-composite of tungsten trioxide nanoparticles andmultiwall carbon nanotubes (MWCNTs). Tungsten trioxide (WO3) is an n-type semiconductor with a reported band gap of about 2.6–2.8 eV. The intrinsic conductivity arises from its nonstoichiometric composition giving rise to a donor level formed by oxygen vacancy defect in thelattice [4]. The WO3 nanoparticles were synthesized by precipitation reaction between the sodium tungstate dihydrate and nitric acid. The constructed sensor was applied for determination of theophylline by adsorptive stripping differential pulse voltammetry. Theophylline showed a well-defined oxidation peak at themodified electrode in sulfuric acid solution which the peak current is much higher than that at thebare GCE and MWCNT-modified GCE. The results showed that the electrochemical oxidation of theophylline on the modified electrode was diffusion-controlled. The effects of scan rate, electrolyte solution, pH, accumulation condition and amounts of MWCNT and nanoparticles were optimized. Under optimizedconditions, the calibration curve was linear in the concentration ranges of 2.0 × 10-8 – 2.0 × 10-5 M with a detection limit of 8.0 × 10-9 M. This modified electrode was used as a sensor for determination of theophylline in pharmaceutical formulation and blood serum samples with satisfactory results.

Keywords:

Tungsten trioxide , Theophylline , Glassy carbon electrode , Carbon nanotubes , Adsorptive differential pulse voltammetry