Novel potentiometric membrane sensor for selective determination of aluminum(III) ions

poly(vinyl chloride) matrix membrane sensor incorporating 7-ethylthio-4-oxa-3-phenyl-2thioxa-1,2-dihydropyrimido[4,5-d]pyrimidine (ETPTP) ionophore exhibits good potentiometric response for Al3+ over a wide concentration range (10-5 to 10-1M) with a slope of 19.5mV per decade. The sensor response is stable for at least 1 month. Good selectivity for Al3+ in comparison with alkali, alkaline earth, transition and heavy metal ions and minimal interference are caused by Hg2+ and Pb2+ which are known to interfere with other aluminum membrane sensors. The ETPTP-based sensor is suitable for use in aqueous solutions of pH 2.25-3.25 and in partially non-aqueous medium with up to 15% (v/v) organic content. The proposed sensor is used for potentiometric titration of HPO42- with Al3+ and for direct potentiometry of Al3+ content of some rocks.