Flow injection potentiometry by poly(vinyl chloride)-membrane electrodes with substituted azacrown ionophores for the determination of lead(II) and mercury(II) ions
School of Chemistry, University of New South WalesSydney, NSW 2052Australia.Department of Physical Sciences, University of Tasmania, Launceston, PO Box 1241Tasmania 7250Australia.
A flow cell with a poly(vinyl chloride) (PVC) neutral-ionophore liquid-membrane ion-selective electrode has been developed for flow injection potentiometry (FIP). The flow system was optimised and five substituted azacrown ethers: 7,16-dithenoyl-1,4,10,13-tetroxa-7,16-diazacyclooctadecane (DTODC), 7,16-di-(2-thiopheneacetyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTAODC), 7,16-dithenyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DTDC), 1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TC) and 4,7,13,16-tetrathenoyl-1,10-dioxa-4,7,13,16-tetraazacyclooctadecane (TTOTC) synthesised and investigated as the ionophores in Pb2+ (DTAODC, TTOTC) and Hg2+ (DTDC, DTODC, TC, TTOTC) selective electrodes. The short contact times between analyte and ionophore in FIP allow the measurement of a strongly complexing 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 groups (TTOTC and DTODC) a carrier of 10 mM potassium nitrate was found to 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-selective electrode, pHg=3.0 to 5.5 with a slope of 28.4 mV decade−1. Highly 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 Pb2+ and 30 samples h−1 for Hg2+.