Enzymatic determination of urea in water and serum by optosensing flow injection analysis

Abstract

Reflectance spectrophotometry was applied to the flow injection measurement of pH in order to perform an assay of urea in water and serum samples via the enzymatic (urease) degradation of urea to ammonia and hydrogen carbonate. Detection is based on commercial non-bleeding acid-base indicator papers situated in the flow stream of an integrated micro-conduit at the tip of a fibre-optic bundle. The sample and reagent are injected via a split-loop injection technique. The serum is analysed by a stopped-flow kinetic measurement to avoid errors in measurements due to the variability in the background sample pH.