Water Analysis : To Estimate Amount of Nitrite Nitrogen In Given Water Sample

INTRODUCTION:
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.
PRINCIPLE:
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.
REQUIREMENTS:
  •  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.
PROCEDURE:
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.

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