Potentiometric and voltammetric responses of carbon fibre electrodes

The potentiometric response of several carbon fibres to hydrogen ion concentration (ph) was investigated. The effects of electrochemical pretreatment and the presence of complexes in the sample solution were studied. In solutions free of complexing anions, the response of pristine fibres ranged from 42.0 to 58.0 mV ph^?1, with a mean of 48.5 mV ph^?1. After electrochemical pretreatment, a mean slope of 52.0 ± 2.0 mV ph^?1 was obtained. In the presence of EDTA, Tris, citrate, oxalate and tartrate, slopes of 59.0 mV ph^? were obtained with pretreated fibres compared with zero slopes or highly curved plots obtained in the absence of pretreatment. The differential pulse voltammetry of iron (III) in a peroxide-containing electrolyte and of molybdate in nitrate- and chlorate-containing electrolytes was examined. At a conventionally sized glassy carbon electrode, the effect on the peak current of increasing the concentration of these ions was broadly in line with depolarizer/electrolyte systems in which catalytic currents occur. At carbon fibre electrodes, these catalytic currents were either absent (for molybdenum/nitrate and iron (III)/peroxide) or severely diminished (for molybdenum/chlorate).