Urea determination in milk by a differential pH technique

Abstract

A differential pH method for the routine determination of urea in milk is presented. The measure is based upon a single enzymatic reaction, the urea hydrolysis by urease, which causes a pH variation directly proportional to the urea content in the milk sample. No sample pretreatment is required. Repeatability expressed as a coefficient of variation was 0.85 % at a level of 416 mg·urea·L-1. Recovery of added urea averaged 99.4 %. The preservatives Bronopol and sodium azide at a ten times higher level than recommended did not affect the results. Comparison with the manual enzymatic French reference method showed a very good agreement. The method is very simple, accurate and rapid. © Inra/Elsevier, Paris.