While the nitrite content of plants is usually extremely low because of its toxicity, the determination of nitrite is currently used for the determination of the nitrate assimilating enzyme, nitrate reductase, nitrite being the product of the reaction.

1. Principle

The method of nitrite determination is based on the reaction between sulphanilamide and nitrous acid with the formation of the diazo compound which reacts with naphthylamine to form a red azo dye that absorbs at 540 nm.

2. Procedure

• To 2 ml of nitrite containing extract, add:

0.5 ml of 1% sulphanilamide prepared in HC1 3 m and

0.5 ml of 0.02% dichlorhydrate of N-l naphthylethylenediamine

• After 20 min of incubation, read the absorbance at 540 nm against a blank.

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