Nitrite is an intermediate oxidation state of nitrogen both in the oxidation of ammonia to nitrate & in the reduction of nitrate. Such oxidation & reduction may occur in waste water treatment, water distribution system & natural water. Nitrite can enter a supply system through it use as a corrosion inhibitor in industrial process water.
Nitrite is the actual etiological agent at methemoglobimia. Nitrous acid which is formed from nitrite in acidic solution can react with nitro samines , many of which are known to be carcinogens.
Nitrite is determined through formation of reddish purple azo dye produced at pH 2.0 to 2.5 by coupling diazotize sulphanilamine with N’ (1- napthyl) ethyl diamine dihydrochloride (NED). The applicable range of the method for photometric measurement is 10-10,000 micro gram NO2/l. Photometric measurement can be made in the range 5 to 50 µg N2/l, if a 5cm light path & a green color filter are used. Higher nitrite conc. Can be determined by diluting a sample with nitrite free D/W. The measurement is taken at 543nm using spectrophotometer.
- Nitrite frees D/W.
- Water sample.
- Drinking water &
- Waste water
- Color reagent.
1. 85% phosphotic acid 100 ml.
2. Sulfonilamide 10 gm
3. Dissolved property in 800ml D/W.
4. NED hydrochloride 1 gm.
5. Mix & final vol. 1000ml with D/W.
6. Solution is stable for 1 month.
- When stored in dark bottle in refrigerator.
- Stock nitrite solution. (NaNO2 1.232g)
(1ml = 250 µg N)
- D/w 1000 ml
- Preserve with 1ml CHCl3.
- Intermediate nitrite solution.
- Stock nitrite solution 50ml.
- D/W 250 ml.
(1ml = 50 µg N)
- Standard (working) nitrite solution.
- Intermediate nitrite solution 10ml.
- Make final vol. 1000ml with D/W
(1ml = 0.5 µg N)
- Prepare fresh.
- Test tubes – 11
- Pipettes 1 ml & 10 ml
- Spectrophotometer & quates.
Take different aliquotes of std. nitrite solution form 0.2, 0.4,…….. 1 ml.
- In blank do not add std. solution.
- Prepare 3 aliquotes of unknown sample.
- Add D/W in all tubes to make final vol. 10 ml.
- Add 0.2 ml color reagent in all tubes.
- Incubate all the tubes at room temp. For 10 min.
- Take O.D. of all tubes at 543nm using blank as a reference.
- Prepare a std. curve by plotting absorbance of std. against nitrite nitrogen (µ gms) of std. & find out conc. Of nitrite present in unknown sample.
- Note down the result & give your conclusion.