However, it is a weaker bidentate ligand as the nitrogen atom in the naphthylamine group is weakly coordinating due to the dispersal of charge by resonance.

[3] N-(1-Naphthyl)ethylenediamine dihydrochloride is widely used in the quantitative analysis of nitrate and nitrite in water samples by colorimetry.

It readily undergoes a diazonium coupling reaction in the presence of nitrite to give a strongly colored azo compound.

With nitrous acid as the limiting reagent, the azo coupling reaction produces an azo dye quantitatively with respect to the nitrite ions: The diazo compound formed accounts for the red coloration typical for a positive result.

The color intensity of the resulting solution is then measured by a colorimeter and checked against a calibration curve to determine the nitrite ion concentration.