Pb(II) sensor based on the membrane of 3,4,4a,5-tetrahydro-3-methylpyrimido[ l,6-a] benzimidazole-l (2H) thione in PVC matrix

Abstract

3,4,4a,5-Tetrahydro-3-methylpyrimido [1 ,6-a] benzimidazole- l (2H) thione (TMPB) has been synthesized and investigated as electroactive phase of membranes for use as Pb²⁺ selective electrode. PVC based membranes of TMPB have been prepared without plasticizer and with a number of plasticizers and investigated. Of the various plasticizers used, tris (2-ethylhexyl)phosphate (TEP) has been found to improve the performance of the membrane significantl y. The membrane having the composition of TMPB:PVC:TEP as 1:40:10 has been found to perform best . The electrode having such a membrane responds linearly to Pb²⁺ over a wide concentration range, 1.9×10^-5- 1.0×10^-1 <i>M, </i>with a slope of 28.5 mV/decade of concentration and small response time of 20 s. The electrode can work over a <i>p</i>H range of 2 to 5.7 and also in partially non-aqueous media. Selectivity coefficient values revealed that the electrode is sufficiently selective over a large number of mono, bi- and trivalent metal cations. It is found to have a life time of one month and could also be used as indicator

electrode in the potentiometric titration of Pb²⁺ with EDTA.