Determination of Urea-N by Steam Distillation

A freshly prepared 5% water extract of commercial ground split pigeon pea, (Cajanus cajan) served as a good source of urease and 5 ml of the extract completely hydrolyzed urea in two hours. NH₄-N and urea-N in a mixture of the solution can be determined separately by steam distillation with MgO suspension in a Pregl-Parnas Wagner steam distillation apparatus, before and after hydrolysis with pigeon pea extract. Hydrolysis of urea was inhibited by the salts NaCl, KCl or Na₂SO₄, at concentrations more than 0.2 N in the medium but it was so at acid concentration even as low as 0.02 N. Soil extracted with KCl-HCl or Na₂SO₄-H₂SO₄ needs to be suitably diluted and neutralized before hydrolysis of urea.