FLOW-INJECTION POTENTIOMETRY BY POLY(VINYL CHLORIDE)-MEMBRANE ELECTRODES WITH SUBSTITUTED AZACROWN IONOPHORES FOR THE DETERMINATION OF LEAD(II) AND MERCURY(II) IONS

A flow cell with a poly(vinyl chloride) (PVC) neutral-ionophore liquid -membrane ion-selective electrode has been developed for flow injectio n potentiometry (FLP). The flow system was optimised and five substitu ted azacrown ethers: 7,16-dithenoyl-1,4,10,13-tetroxa-7, 16-diazacyclo octadecane (DTODC), heneacetyl)-1,4,10,13-tetraoxa-7,16-diazacycloocta decane (DTAODC), henyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane ( DTDC), 1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TC) and enoyl-1,1 0-dioxa-4,7,13,16-tetraazacyclooctadecane (TTOTC) synthesised and inve stigated as the ionophores in Pb2+ (DTAODC, TTOTC) and Hg2+ (DTDC, DTO DC, TC, TTOTC) selective electrodes. The short contact times between a nalyte and ionophore in FIP allow the measurement of a strongly comple xing ion such as Hg2+ that saturates the electrodes in batch analysis, or in continuous flow analysis that comes to a steady state, For the mercury-selective electrodes with ionophores with amide functional gro ups (TTOTC and DTODC) a carrier of 10 mM potassium nitrate was found t o increase the speed of response and recovery to baseline, The linear calibration range for a DTAODC lead-selective electrode was pPb=2.0 to 5.0 with a slope of 32.5 mV decade(-1) and for a TTOTC mercury-select ive electrode, pHg=3.0 to 5.5 with a slope of 28.4 mV decade(-1). High ly reproducible measurements were obtained (RSD <2%) at a flow rate of 3.0 ml min(-1) giving a typical throughput of 40 samples h(-1) for Pb 2+ and 30 samples h(-1) for Hg2+. (C) 1998 Elsevier Science B.V. All r ights reserved.