ALL PURPOSE INDICATOR ELECTRODE FOR POTENTIOMETRIC TITRATIONS OF BOTH CATIONIC AND ANIONIC TYPE DRUGS

Membrane electrodes of PVC, graphite and all-solid-state constructions made with ion-pair complex of quaternary ammonium, phosphonium or arsonium with various anionic species including tetraphenylborate, hetero-poly acid and picrolonate have been studied comparatively as all-purpose indicator electrode for potentiometric determinations of both cationic and anionic type drugs with different titrants. The cetyltrioctylammonium phosphotungstate electrode of all-solid-state construction was found to be the most suitable indicator electrode for the titration of 16 cationic and 6 anionic drugs with sodium tetraphenylborate and sulphuric acid. The average recovery for 33 samples in the concentration range of 0.7 μg/ml～1.8 mg/ml was 100.3%, the standard deviation being 0.63%. The change in EMF at the end-point reached up to 150～00mV. The electrode can be used for titration of another drug after 5-rain re-conditioning. The electrode function deteriorates in the order of cetyltrioctylammonium>cetyltriphenylphosphonium>cetyltriphenylarsonium, cetyltrioctylammonium>cetyltributylammonium>cetyltrimethylammonium>tetrabutylammonium>tetraethylammonium and phosphotungstate>tetraphenylborate>picrolonate. Pre-conditionning can be accelerated by benzalkonium.