Determination of Nitrite Nitrogen

Aim
To determine the nitrite nitrogen of the given sample of water.

Principle
The nitrite concentration is determined through the formation of a reddish-purple azo dye produced at pH 2.0–2.5 by the coupling of diazotised sulphanilic acid with N-(1-naphthyl)-ethylenediamine dihydrochloride.

Apparatus
  1. Spectrophotometer
Reagents (» click to check the preparation of reagents)
  1. Sulphanilamide reagent
  2. N-(1-naphthyl)-ethylenediamine dihydrochloride solution
  3. Hydrochloric acid (1+3)
  4. Stock nitrite solution
  5. Standard nitrite solution
Procedure
  1. To 50 ml clear sample neutralised to pH 7, add 1ml sulphanilamide solution.
  2. Allow the reagent to react for a period of 2–8 minute.
  3. Then add 0.1ml of 1-naphthyl ethylenediamine solutions and mix immediately.
  4. Measure the absorbance of the solution after 10 minute at 543 nm at 1 cm light path.
  5. Prepare standard calibration curve as in any other case.
  6. By noting the absorbance of an unknown sample, the concentration of nitrate can be determined
Calculation
Nitrite N in mg/L = mg Nitrite N
mL of sample


Observation
The observation is presented in Tables A and B respectively


Table A: Observation for calibration


Table B:


Results