Figure 2. Potentials obtained within 5 min after exposure to various concentration of procaine were measured in the procaine-sensitive microelectrode and plotted against a logarithm of procaine concentrations. The potentials of procaine-sensitive microelectrodes responded linearly with the slope of 50 to 59 mV/log[procaine] at concentrations that ranged from 0.2 to 5 mM of procaine but deviated gradually from the linear response and decreased the slope at <0.2 mM.