Anal. Chem. 1994,66, 2250-2259
Response Mechanism of Polymer Membrane-Based Potentiometric Polyion Sensors Bin Fu,t Eric Bakker,?Jong H. Yun: Victor C. Yang,* and Mark E. Meyerhoff'J Department of Chemistry and College of Pharmacy, The University of Michigan, Ann Arbor, Michigan 48109 The potentiometricresponsemechanismof a previouslyreported polymer membrane-based electrode sensitive to the polyanion heparin is established. Based on transport and extraction studies, the heparin response is attributed to a nonequilibrium change in the phase boundary potential at the sample/membrane interface. While true equilibrium polyion response, obtained for low heparinconcentrations only after very long equilibration times (>20 h), yields the expected Nernstian response slope of
