A novel potentiometric sensor for selective determination of theophylline: Theoretical and practical investigations

A novel theophylline potentiometric sensor is prepared, characterized and used in pharmaceutical analysis. The sensor is based on a PVC membrane containing dibutyl phthalate as plasticizer, 2,6-bis(phenyl)-4(phenyl)3H-thiopyran (PPT) as ionophore and oleic acid (HOA) as additive. A linear response in the range of 1.0 × 10−6 to 1.0 × 10−2 M of theophylline with a slope 54.5 ± 0.4 mV per decade was established. The optimum pH range was 5.3-7.3 and the lower detection limit was 5.5 × 10−7 M of theophylline. The electrode displays a good selectivity for theophylline with respect to a large number of common foreign inorganic and organic species, amino acids and drugs. The membrane sensor was successfully applied to the determination of theophylline in its tablets. A theoretical study based on the optimum angle and distance between theophylline and PPT molecules was conducted. These investigations were carried out based on ab initio calculations, to estimate the pair wise interaction energy between the two molecules.