A CHLORIDE ION-SELECTIVE SOLVENT POLYMERIC MEMBRANE-ELECTRODE BASED ON A HYDROGEN-BOND FORMING IONOPHORE

A chloride-selective solvent polymeric membrane electrode based on a n eutral hydrogen bond forming ionophore, poly(vinyl chloride) (PVC), th e plasticizer 2-nitrophenyl octyl ether (o-NPOE), and cationic sites ( 50 mol %, relative to the ionophore) is described. At pH 7.0 (HEPES bu ffer), this electrode responds to chloride in a linear range from 10(- 5) to 10(-2) M with a slope of (-54.0 +/- 1.0) mV/decade and a detecti on limit of (6.5 +/- 3.0) x 10(-6) M. As compared to conventional anio n-exchanger electrodes, the interference of SCN-, Br-, NO3-, I-, and e ven salicylate is considerably reduced, as shown by the selectivity co efficients determined with the matched potential method (MPM) in the c hloride concentration range 10(-2.34)-10(-2.04) M (log KPCl,jpot (MPM) : Sal(-), +1.8; SCN-, +1.6; NO3-, +0.7; I-, +0.5; Br-, +0.4). Because the discrimination of the more hydrophilic anions SO42-, HSO3-/SO32-, OAc-, HCO3-, and H2PO4-/HPO42- is too large for a determination of acc urate selectivity coefficients in this high chloride concentration ran ge, corresponding values for the range 10(-5.00)-10(-4.70) M Cl- have been determined (log K-Cl,j(pot) (MPM): SO42-, -1.2; HSO3-/SO32-, -2.0 ; OAC-, -2.3; HCO3-, -2.6; H2PO4-/HPO42-, < -3.5), showing here, too, a good selectivity for Cl-. The chloride ion concentration in certifie d control horse serum was determined by the standard addition method a s 102.1 mM with a coefficient of variation of 0.42% (n = 6). This resu lt is in excellent agreement with the certified value of 102.3 mM, as determined by coulometry, and demonstrates the applicability of this s ensor for measurements in biological samples. The selectivity upon sto rage of the electrode in buffer solution for 4 weeks decreases but is stilt considerably better than that for a freshly prepared anion-excha nger electrode.