Electrical Stimulation with Pt Electrodes. IV. Factors Influencing Pt Dissolution in Inorganic Saline

Trace analysis has shown that Pt electrodes can suffer appreciable dissolution when used to apply biphasic current pulses of the type used in neural stimulation. The dissolution occurs even under conditions where other irreversible faradaic reactions, e.g., H2O electrolysis, are avoided. In the present study, factors influencing the dissolution of Pt electrodes during biphasic pulsing in neutral inorganic saline have been examined. The findings are consistent with the behaviour of Pt electrodes reported in other inorganic media. In a given test, the quantity of Pt dissolved was found to be a linear function of the aggregate anodic or cathodic charge injected. Therefore, dissolution 'rates' can be conveniently expressed in terms of nanograms of Pt per coulomb injected, e.g., 100 ng C-1. Most of the Pt went into solution as Pt (II) species, so the above rate would correspond approximately to 100 p.p.m. of the anodic charge per pulse. For anodic-first (AF) pulses, charge density was the major factor controlling dissolution, whereas for cathodic-first (CF) pulses, pulse duration had the greater influence. Depending on the polarity (AF or CF), charge density, and duration of the biphasic pulse, the dissolution rate for smooth bead electrodes ranged from 30 to 300 ng C-1. Lower rates were achieved with platinized electrodes but in the absence of organic solutes, it is unlikely that Pt dissolution can be completely suppressed.