Method for NO2 Measurement in Ambient Air (Jacob and Hochheiser Method)

Principle: NO₂ in air is collected by scrubbing a known volume of air in a solution of sodium hydroxide-sodium arsenite solution. The absorbed NO₂ is determined as the Azo dye by “diazotizing” it with sulphanilamide in the presence of phosphoric acid and “coupling” it with NEDA

Range & Sensitivity: The range of the method is 9-750ug/m3. The analytical range is 1-2ug in a 50ml final solution.

Interferences 

  Sulfur dioxide is a major interferent. Its interference can be removed by adding H₂O₂.

Reagents Required

Absorbing Solution 0.1N NaOH containing sodium arsenite.

NO₂ Standard  Solution is prepared from sodium nitrite salt

Range :   9- 420µgNO₂/ml

(50 ml reagent flow rate 0.2 lpm duration 24 hrs at sampling efficiency of 0.82)

Detection limit  0.04 to 2.0 µg/ml

Preparation of Reagent

A. For Sampling:

  Absorbing Reagent: Dissolve a 4.0gm Sodium Hydroxide and 1.0gm  Sodium Arsenite  in 1 liter distilled water.

  Caution: Arsenic compounds are highly toxic; avoid contact with skin and especially with eyes. Wash hands after handling it. Do not take internally.

B. For Analysis:

  1. Hydrogen Peroxide Solution: Dilute 0.2ml of 30% H₂O₂ to 250ml with distilled water.

  2. Sulfanilamide Solution: Dissolve 20gm of Sulfanilamide in 700ml-distilled water and mix 50ml of 85% Phosphorice acid, make it upto 1 litre.

  3. NEDA Solution: Dissolve 0.5gm of NEDA in 500ml of distilled water.

Note: these solutions are stable for one month, if refrigerated and protected from light.

Sodium Nitrite Solution

Preparation of Calibration Curve (NO₂)

1. Pipette  0.0 (blank), 2.0, 4.0, 6.0, 8.0, 10.0ml of I µg NO₂/ml standard nitrite solution in a series of 50ml volumetric flask.

2. Add sufficient Sod. Hydroxide, sodium arsenite solution to each tube to bring the volume upto 10ml.

3. Add 1 ml Hydrogen Peroxide solution

4. Add 10 ml of sulfanilamide solution

5. Add 1.4 ml of NEDA solution

6. Make upto 50ml with distilled water

7. Mix thoroughly

8.Measure the absorbance at 540nm after 10min against the blank reagent. Plot the absorbance verse concentration at different strengths

Analysis (NO₂)

1. Mix thoroughly the sample of bottles by shaking several times.

2. Take two  volumetric flask (blank and sample)

3. Pipette 10 ml unexposed absorbing reagent in Blank  and 10ml exposed absorbing reagent (Sampled solution) in volumetric flask.

4. Add 1 ml of Hydrogen Peroxide solution

5. Add 10 ml of sulfanilamide solution

6. 1.4 ml of NEDA solution

7.Make up to 50 ml with distilled water

  Note: Mix thoroughly after addition of each reagent

8.   Measure the absorbance at 540 nm after 10 min against the blank reagent by using Spectrophotometer.