Ehrlich aldehyde reagent

Ehrlich s aldehyde test can be used to confirm a diagnosis of acute intermittent porphyria. Equal volumes of urine and Ehrlich s reagent are mixed a pink colour indicates raised urinary concentration of either porphobilinogen or urobilinogen. In acute intermittent porphyria, raised porphobilinogen is present and the pink precipitate formed is insoluble in chloroform. 

Tryptophane Tests.—(i.) Add 3 drops of Ehrlich s aldehyde reagent to about 2 ml. of protein solution, followed by excess (3-5 ml.) of concentrated hydrochloric acid. Heat gently to boiling. A violet colour develops if the protein contains tryptophane. Add 1-3 drops of 0-1 per cent, hydrogen peroxide. The colour changes to deep blue. Excess of the oxidiser rapidly bleaches the pigment. 

Urobilinogen, unlike urobilin, gives an immediate red colour with Ehrlich s aldehyde reagent in acid solution (p. 149 ). 

Benzylidine Test.— The solutionis acidified with a few drops of HCl, and then a few drops of Ehrlich s aldehyde reagent (3 per cent, p-dimethylaminobenzaldehyde in 20 per cent. HCl) are added. An intense yellow colour develops if urea be present. 

A1M.yde Test.— Add 3-5 drops of Ehrlich s aldehyde reagent (p. 149) to 2 ml. of water. Acidify with 3-5 drops of concentrated hydrochloric acid. On addition of a few drops of urine the mixture turns deep yellow owing to formation of a pigment from the urea and the aldehyde. 

Ehrlich s Aldehyde Reagent, 2-3 per cent, p-dimethylamino benzaldehyde in alcohol or in 20 per cent. HCl. Reagent for muco-proteins, indole, indoxyl, urobilinogen, urea, allantoin and (in excess of strong acid) tryptophane and scatole. The reagent in 20 per cent. HCl is almost colourless, and is suitable for the urea and allantoin tests. 

Fundamentally similar to pyrromethene formation are two of the classical colour reactions associated with pyrroles. The redness produced by pyrroles with an acid-moistened pine shaving is due to reaction with aldehydes in the wood, but it is not specific for pyrroles " . Ehrlich s reaction depends on the formation of coloured products by the reaction of a pyrrole with j -dimethylaminobenzaldehyde in acid solution. The nature of the reaction is indicated by the isolation of a salt of the cation (26) after treatment of (27) with the Ehrlich reagent, a carboxyl group being eliminated (26) gives red solutions, the disodium salt of the derived free base produces yellow solutions, and treatment of (26) with excess acid the colourless di-protonated salt . ... 

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