Urea determination in milk by a differential pH technique

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 pretreat- ment 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 man- ual enzymatic French reference method showed a very good agreement. The method is very simple, accurate and rapid. © InralElsevier, Paris