STUDY MATERIAL OF UGC NET (ENVIRONMENTAL SCIENCES)

Analysis Methods forAnalysis Methods for
Measurement of AmmoniaMeasurement of Ammonia
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Method for NHMethod for NH33 Measurement in Ambient AirMeasurement in Ambient Air
(Indophenol Blue Method)(Indophenol Blue Method)
Principle:
NH3 in air is collected by scrubbing a known volume of air in a dilute
solution of sulphuric acid. The ammonium sulphate formed in the
sample is analyzed colorimtrically by reaction with phenol and alkaline
sod.hypochlorite to produce indophenol. The reaction is accelerated by
the addition of sodium nitropruside as catalyst.
Range & Sensitivity:
The range of the method is 20 - 700ug/m3. The analytical range is
0.2ug/ml
Interferences
interfering particulate matter in the air can be removed by filtration of the
air sample.
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(As recommended by CPCB, Govt. of India)(As recommended by CPCB, Govt. of India)
Step I: Preparation of Reagent
A. For Sampling:
Absorbing Reagent: 0.1N Sulphuric Acid
Caution: Sulphuric Acid is highly toxic ;avoid contact with skin and especially with eyes. Wash
hands after handling it.
B. For Analysis:
1. Sodium Nitropruside Solution: Dissolve 2gm Sodium Nitropruside in 100ml distilled water.
2. Buffer Solution: Dissolve 50 gm of Sodium phosphate and 74ml of 6.75 M NaOH in 1 litre of
distilled water .
3. Sodium Hypochlorite Solution: Mix 30ml of 0.1N sodium hypochlorite and 30 ml of 6.75 M
Sodium hydroxide and dilute to 100 ml with distilled water.
4. Phenol Solution : Dilute 20ml of 45% phenol solution with 1ml of 2% Sodium Nitropruside
Solution and dilute to 100ml with distilled water.
C. For Calibration Curve:
1. Ammonia Stock Solution :1000 µg NH3/ml
2. Standard Ammonia Solution :10 µg NH3/ml(Caution: Prepare fresh)

Sampling:
Place 10 ml of absorbing reagent in an impinger
Sample for desired time at flow rate 0.5 – 2.0lpm
After Sampling measure the volume of absorbing
reagent
Makeup the evaporating absorbing reagent with distilled water as initial volume

Continue Sampling:
Transfer sampled absorbing reagent in sample storage
bottle
Go to lab for analysis

Step II: Preparation of Calibration Curve (NH3)
1. Pipette 0.0 (blank), 0.5, 1.0, 1.5, 2.0 of 10µg NH3/ml standard ammonia solution in a
series of 25ml glass stopper graduated cylinder.
2. Make up to 10ml with absorbing reagent
3. Maintain all the solutions and sample at 25 oC(Room temp.)
4. Add 2ml Buffer solution .
5. Add 5ml of working phenol solution .
6. Mix thoroughly and add 3ml distilled water .
7. Add 2.5 ml of working hypochlorite solution and Mix thoroughly .
8. Dilute to 25ml with distilled water ,mix and store in the dark for 30 minutes to develop
colour.
9. Measure the absorbance at 630nm against the field blank reagent.
10. Plot the absorbance verse concentration at different strengths.

Step III: Analysis (NH3)
1. Mix thoroughly the sample of bottles by shaking several times.
2. Take two 25ml glass stopper graduated cylinder. (blank and sample)
3. Pipette 10ml unexposed absorbing reagent in Blank and 10ml exposed absorbing
reagent (Sampled solution) in glass stopper graduated cylinder.
4. Add 2ml Buffer solution .
5. Add 5ml of working phenol solution .
6. Mix thoroughly and add 3ml distilled water .
7. Add 2.5 ml of working hypochlorite solution and Mix thoroughly .
8. Dilute to 25ml with distilled water ,mix and store in the dark for 30 minutes to develop
colour.
9. Measure the absorbance at 630nm against the field blank reagent.

Calculation:
(As – Ab) x CF x1000
Concentration = ---------------------- =µg/m3
Va
As =Absorbance of Sample
Ab = Absorbance of reagent Blank
CF = Calibration Factor
Va = Volume of air Sampled(litre)
=Avg. Flow Rate x Sampling Period

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