Comparative study of potentiometric and amperometric tissue-based electrodes for oxalate

Acetone-precipitated pulp from banana skins is physicall entrapped at the tip of a carbon dioxide gas-sensor and on a hydrogen peroxide sensor probe to determine oxalate potentiometrically and amperometrically in aqueous solution and inurine. The enzyme present in the tissue is oxalate oxidase. The potentiometric response has a slope of 47-50 mV/decade for 1 × 10^-4 M-2 × 10^-3 M oxalate with a detection limit of 2 × 10^-5 M. The amperometric response is linear for 2 × 10^t-5-3 × 10^-4 M oxalate with a dectection limit of 2 × 10^-6 M. Average recoveries of oxalate added to aqueous samples were 96.2% and 98.0%, and average relative standrd deviations were 3.8% and 3.6% for the potentiometric and amperometric systems, respectively. Oxalate was determined in six control urine samples, with relative errors of about 2.5%, by both electrode systems after a simple clean-up.