Novel liquid membrane electrode for selective determination of monohydrogenphosphate

A highly selective and sensitive membrane electrode based on vanadyl salen complex (VS), which responds to monohydrogenphosphate (MHP) ions is described. The response of the sensor is Nernstian over the wide concentration range (1.0 x 10(-1) - 5.0 x 10(-6) M) of MHP. The sensitivity of the electrode is high enough to permit the detection of as little as 0.6 mug/mL of MHP without any significant interference from high levels of other anions. The potentiometric selectivity coefficient data revealed negligible interference from 11 common anions. The electrode has a fast response time (< 25 s), good slope stability at pH 8.2 for a period of at least eight weeks. It was successfully applied for the direct determination of monohydrogenphosphate in fertilizer and, as indicator electrode, in potentiometric titration of Hpo(4)(2-) ion with barium chloride.