In this case the enzyme urease is used to catalyze the hydrolysis of urea into carbon dioxide and ammonia.
Replacement of phenol by 2-phenylphenol reduces interferences by a variety of soil and water constituents and improves color stability at slightly lower pH.
[2] The reagent lacks sensitivity in situations where there may be amines as well as ammonia, however this can be overcome in part by the use of 2-phenylphenol to replace phenol.
An ion selective electrode, or distillation/titration method can often be used in cases where Berthelot chemistry is ineffective.
Berthelot chemistry has also been adapted for the analysis of nitrite and nitrate in soil and water after conversion, typically by reduction with Devarda's alloy, of these species to ammonium.