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Measurement of Nitrite in Water and Wastewater


Measurement of Nitrite in Water and Wastewater

 

ô PURPOSE:

                    To describe the Laboratory standard operating procedure for measurement of Nitrite by Colorimetric Method in Water and Waste Water samples.

                     

ô SCOPE:

                    Applicable to the Laboratory for analysis of Water and Waste Water samples, where measurement of Nitrite is required.

 

ô RESPONSIBILITY:

Lab chemist

:

Analysis of sample for measurement of Nitrite.

Technical Manager

:

Review of activity

Quality Manager

:

Implementation and compliance of SOP.

                     

ô PROCEDURE:

1.     Principle:

·       Nitrite (NO2-)  is determined through formation of reddish purple azo dye produced at pH 2.0 to 2.5 by coupling diazotized sulfanilamide with N-(1-naphthyl)-ethylene-diamine dihydrochloride (NED dihydrochloride).The applicable range of method for spectrophotometric measurements is 10 to 1000 µg NO2- - N/L at 543 nm.

 

2.     Instrument and Equipment:

3.     Spectrophotometer at 543 nm.

 

4.     Reagents:

·       Nitrite free Water- Add to 1 L distilled water one small crystal each of KMnO4 and either Ba(OH)2 or Ca(OH)2 . Redistill in all borosilicate glass apparatus and discard the initial 50 ml of distillate.

·       Color Reagent:  To 800 mL  water add 100 mL 85% phosphoric acid and 10 g Sulphanilamide. After dissolving Sulfanilamide completely add 1  g of N-(1-naphthyl)-ethylene-diamine dihydrochloride.Mix to dissolve,then  dilute to 1  L with water.

5.     Test Method:

·       Removal of Suspended Solids: If sample contains suspended solids, filter through 0-45 µm-pore-diam membrane filter.

·       Color Development: If sample pH is not between 5 and 9, adjust to that range with 1 N HCl or NH4OH as required.To 50 mL sample add 2 mL of Color reagent and mix.

·       Photometric Measurement: Between 10 min measure absorbance at 543 nm.

·       Now, determine the Sulhite concentration from the developed curve.


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