ESTIMATION OF METAL IONS BY MACROCYCLIC MEMBRANE ELECTRODES

Abstract

Polystyrene and Poly (vinyl chloride) based membranes of Ph4(14)tetraene and Me8(14)ane were prepared and explored for their possible use as Cr3+ and Al3+ selective electrodes. The solvent mediators dibutyl phthalate (DBP), dibutyl(butyl) phosphonate (DBBP), tris (2-ethylhexyl) triphosphate (TEP) and tributyl phosphate (TBP) were tried to improve the response characteristics of the electrodes as well as sodium tetraphenyl borate (STB) was also used as anion excluder to minimise the interferences by anions. Membranes having macrocycle, STB and Polystyrene in the ratio (w/w) 4:1:1 showed a linear potential response in the concentration range 3.16 x 10-6 — 1.00 x 10-1 M with a Nernstian slope of 17.3 mV/decade between pH range 3.0 to 6.5 for Cr3+, while the membranes having Me8(14)ane, STB, DBP and PVC in the ratio (w/w) 2:1:7:10 show linearity over a concentration range 1.77 x 10-6 — 1.00 x 10-1 M with a Nernstian slope of 20 mV/decade between pH range 3.0 to 6.5 for Cr3+ and concentration range 1.00 x 10-6 — 1.00 x 10-1 M with a Nernstian slope of 20 mV/decade between pH range 2.5 to 7.0 for A13+. All the electrodes exhibit a fast response time of 15, 15 and 10s, respectively. Their performance is also satisfactory in partially non-aqueous medium. Potentiometric selectivity coefficient values indicate reasonably good selectivity for Cr-3+ and A13± over a number of cations.