Figure 5

The MC3-ISM is highly selective for Cl⁻. The MC3-ISM response was measured in solutions prepared by serial dilution of pure NaCl with no interfering anions (n = 14, black squares reproduced from Fig. 2) or for the NaCl solutions plus 10 mM of the test anion as Na⁺ salts of \({{\rm{HCO}}}_{3}^{-}\) (n = 3, red circles), lactate (n = 3, blue triangle), \({{\rm{PO}}}_{4}^{-}\) (n = 3, green inverted triangle), or SCN^- (n = 3, magenta diamond). A linear fit for the pure NaCl data over a range of 0.1 mM to 100 mM solutions shows a Nernstian response (black line). The cut-off a_Cl in the presence of an interfering anion was determined by the intersection of limiting asymptote and the Nernstian response, as shown by the example for \({{\rm{HCO}}}_{3}^{-}\) (red dashed line). These values were used to calculate the selectivity coefficient (see Methods).