Berthelot's reagent

Berthelot's reagent is an alkaline solution of phenol and hypochlorite, used in analytical chemistry. It is named after its inventor, Marcellin Berthelot.

Ammonia reacts with Berthelot's reagent to form a blue product which is used in a colorimetric method for determining ammonia.

The reagent can also be used for determining urea. In this case the enzyme urease is used to catalyze the hydrolysis of urea into carbon dioxide and ammonia. The ammonia is then determined with Berthelot's reagent.

There is a modified Berthelot reagent in which the phenol is replaced by sodium salicylate. This has been used for blood urea nitrogen (BUN) determinations.

Berthelot's reagent is not very specific (it detects amines as well as ammonia) so it may be preferable to use an ion selective electrode.