Figure 3.

Calibration curve for the Cd²⁺ microelectrode in Cd(NO₃)₂ solutions containing a background of 100 mm KNO₃ and 2 mm Mg(NO₃)₂ (i.e. artificial cytoplasm). The electrode response (in millivolts) was arbitrarily defined as 0, as described in Figure 1. The solid line is the linear regression for the experimental points. The sensitivity (slope) is equal to 29 mV/dec (r²= 0.995 excluding the two lowest activity points). The dotted line represents the theoretically expected response for a Cd²⁺-selective microelectrode with an ideal Cd²⁺ selectivity, as calculated by the Nernst equation.