NOVEL POLYMERIC MEMBRANE ELECTRODES FOR SELECTIVE DETERMINATION OF TRIMETHOPRIM

Trimethoprim (TMP) ion selective PVC membrane electrodes based on the ion-pair complexes of trimethoprim cation with either ammonium reineckate I or sodium tetraphenyl berate (II)were prepared, using dioctyl phthalate (DOP) as the plasticising mediator. The basic analytical parameters of these electrodes were evaluated according to IUPAC recommendations. These electrodes gave linear response with Nernstian Slope (57 and 58 mV / decade) for electrode I and electrode II, respectively. The potentiometric selectivity data show negligible interference from the various species investigated. These electrodes have fast response time ( < 30s), good slope stability over the pH range 2.0-5.7 or 2.0-5.5 for period of 45 or 60 days for electrode I and II, respectively. The standard electrode potentials were determined at different temperatures and were used to calculate the isothermal coefficient of these electrodes. Direct potentiometric determination of trimethoprim hydrochloride (TMPCI) in aqueous solutions and in pharmaceutical formulations using the proposed electrode systems give good results. The obtained results are better than those obtained by the British Pharmacopoeia's method.