Chemistry of water -Part 23-

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Nitrite titration:

Nitrite quickly turns into nitrate by bio-oxidation, so it is calibrated immediately after obtaining the water sample. And in the event that it is not possible to calibrate it immediately after obtaining the sample, mercury chloride must be added, and the sample is kept at a temperature of 4 °C.

  • 1- Zambelli's reagent method:

Sulfanilic acid, with nitrites ions (NO2-) and in the presence of ammonium and phenol ions, forms a yellow complex, where the nitrite concentration and colour intensity in the sample are proportional.


Sample of Sulfanilic acid

By dissolving 260 ml of hydrochloric acid (with a density of 1,19) in distilled water and adding 5 grams of sulfanilic acid (C6H7NO3S) and 7,5 grams of phenol, Zambelli's reagent is prepared. 135 grams of ammonium chloride is added to the mixture after it is gently heated until complete dissolution, then the volume is expanded to a liter by adding distilled water.

Zambelli's reagent (2 ml) is added to 50 ml of the aqueous sample that we want to analyze, the mixture is mixed well and then left for ten minutes. Then we add a volume equal to 2 ml of ammonium hydroxide before we use the spectrophotometer at the wavelength of 435 nm to measure the absorbance of the solution. The results are compared with a standard curve prepared in the same way, but using solutions of known concentration. This method is used for samples containing a concentration of more than 50 micrograms per liter of nitrite ions.

References:

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