Lead (II)-selective membrane electrodes based on 4,7,13,16-tetrathenoyl-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane

Lead(II)-selective PVC membrane electrodes based on 4,7,13,16-tetrathenoyl-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TTOTC) as ionophore were prepared. The optimum composition of the membrane was 30 wt% poly(vinyl chloride), 67 wt% 2-nitrophenyl octyl ether plasticizer, 3 wt% ionophore with added lipophilic salt potassium tetrakis(p-chlorophenyl)borate at 50 mol% with respect to the ionophore concentration. The electrodes exhibited near theoretical Nernstian slopes (31.9 ± 0.4 mV/per decade) in the activity range log10[a(Pb2+)]=-5.3 to log10[a(Pb2+)]=-3.0 and with a detection limit log10[a(Pb2+)]=-5.7. Compared to the previously reported disubstituted, diazacrown 7,16-dithenoyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane the electrodes based on TTOTC showed much better selectivity particularly towards alkali and alkaline metal ions. However, mercury and silver remain the major interferences. The electrodes were used in potentiometric titrations of Pb2+ and the determination of Pb2+ in synthetic soil samples.