The reagent is typically provided in two parts: 
* A mixture of 2% sodium nitroprusside and 2% acetaldehyde in water (solution A)
* A solution of 2% sodium carbonate in water (solution B)
Separate storage of the aldehyde and base are necessary to prevent aldol polymerisation of the aldehyde.
When exposed to an amine, reaction with acetaldehyde produces the enamine, which subsequently reacts with sodium nitroprusside to the imine. Finally, the iminium salt is hydrolysed to the bright blue Simon-Awe complex.
Acetaldehyde can be replaced with acetone, in which case the reagent detects primary amines instead, giving a purple coloured product.