Potentiometric CO32− response of an ISE based on a liquid membrane with perfluoroperhydrophenanthrene doped with (1) 1.0 mM cationic sites, 1, and 1.5 mM ionophore Mn-1, (2) 2.0 mM cationic sites, 1, and 1.5 mM ionophore Mn-1, and (3) 1.0 mM anionic sites, 2, and 4.0 mM ionophore Mn-1. Sample solutions contained sodium bicarbonate buffered with 10 mM Tris-H2SO4 to pH=8.75. Response curves were shifted vertically relative to one another for enhanced clarity.