An improved diacetyl reaction for the estimation of urea in blood

The diacetyl or carbamido reaction of Fearon (1939) has been utilized by Ormsby (1942) and by Barker (1944) for the estimation of urea in biological fluids. Archibald (1945) has used the homologue of di- acetyl, ot-i8onitrosopropiophenone (the monoxime of benzoyl-acetyl) for a similar method which has the advantage that the colour obtained is red instead of yellow. By analogy with the Barritt (1936) reaction, in which ac-naphthol is used to enhance the colour obtained from creatine and diacetyl in alkaline solution, it was considered* possible similarly to enhance the diacetyl-urea reaction. The observation of Barker (1944) that thymol interfered with this reaction lent support to the hypothesis. Phenols were first tried but produced precipitates. With aromatic amines the colour produced was orange or red and not yellow, whilst diphenylamine and its derivatives produced an intense magenta colour. The reaction with N-phenylanthranilic acid (di- phenylamine-2-carboxylic acid) has been studied in detail and adapted for the estimation of urea in blood.