a -NAPHTHYLAMINE SOLN

α-Naphthylamine Solution is used with Sulphanilic Acid for the determination of nitrate reduction by bacterial strains, particularly members of Enterobacteriaceae. This test is used for the identification of microorganisms based on their ability to reduce nitrate (NO₃) to nitrite (NO₂) or further reduce it to other end products.
Nitrate-reducing organisms convert nitrate to nitrite in the reaction. Sulphanilic Acid reacts with Nitrite to form a diazonium salt. This intermediate, when reacted with α-Naphthylamine, gives a water soluble azo dye, exhibiting a characteristic pink to purple colour.
The reagent is valuable as an adjunct to differentiate bacteria and should be employed with other biochemical tests for the identification of the organism. Nitrate Agar or Nitrate Broth with low amounts of nitrite is recommended to minimize the possibility of false reactions. If nitrite reaction is negative, it is determined by zinc dust that either nitrate is reduced to nitrite stage further or not. Too much zinc should be avoided because it can also give false results. Proper specimen handling and established laboratory procedures should be followed during testing.

Used with Sulphanilic Acid to detect nitrate reduction by bacterial strains through a visible pink-red colour reaction.