Urea pH electrodes: characterisation and optimisation for plasma measurements

Abstract

A potentiometric urea enzyme electrode is reported where consumption of H⁺ by the urease-catalysed degradation of urea is followed at a glass pH electrode. The response of the electrode in both weak buffers and diluted plasma is described, and the special conditions needed for plasma assay are outlined. Response times were 1–3.5 min. The use of 0.002 M phosphate assay buffer gave linear calibration graphs up to 5 × 10^–4M urea. The response to plasma diluted 1 + 49 or 1 + 999 initially proved unreliable, but corresponded to that in aqueous standards when allowance was made for background pH variation using an auxiliary pH electrode.