Improvements in the determination of urea using diacetyl monoxime; methods with and without deproteinisation

A rapid and reproducible method is described for measurement of urea in biological materials (after deproteinisation) and in serum (without deproteinisation). Urea is colorimetrically determined with diacetyl monoxime and thiosemicarbazide in the presence of sulphuric acid, phosphoric acid and ferric chloride. The sensitivity of the colorimetric reaction and stability of the colour are enhanced over existing related procedures and the serum blank diminished, enabling urea to be precisely measured in micro amounts (1–5 μl) of serum.