Comparison of Oxalate Oxidase Enzyme Electrodes for Urinary Oxalate Determinations

Abstract

Enzyme electrodes for oxalate were constructed by immobilizing oxalate oxidase enzyme (E, C, 1,2,3,4) on both potentiometric carbon dioxide and amperometric hydrogen peroxide sensors. These systems were optimized, and the response characteristics of the two biosensors examined in a comparison study. Areas investigated include linear range, calibration curve slope, response time, limit of detection, and lifetime. Selectivity studies were carried out with the system and showed no measurable response to millimolar levels of various L-amino acids, metal ions or ascorbic acid. This comparison was extended into the choice of an optimal sensor for urinary oxalate determinations with minimal sample pretreatment. The peroxide sensor performed best in urine samples, allowing for the 1:40 dilution necessary to minimize the effect of any interferents present. At this or greater dilution, the recovery of standard additions of oxalate averaged 95.5%, with an average relative standard deviation of 4.9%. The system retained its activity throughout two weeks of continued use.