Reference method for measuring emissions of nitrogen oxides from stationary sources: chapter 6

6 Reagents

6.1 Purity of Reagents

Reagent-grade chemicals meeting the American Chemical Society Standards for purity shall be used throughout. Where no such standards exist, other reagents may be used providing their use does not decrease the accuracy of the determination.

6.2 Water

Deionized or distilled and nitrate-free as demonstrated by a low blank.

6.3 Sampling Train

  • 6.3.1 Hydrogen Peroxide (3%). Dilute 10 ml of concentrated H2O2 (30%) to 100 ml. Prepare fresh daily.

  • 6.3.2 Sulphuric Acid (sp. gr. 1.84). Concentrated H2SO4, minimum assay 95%.

  • 6.3.3 Absorbing Solution. Prepare absorbing solution by adding 3 ml of concentrated sulphuric acid ( H2SO4) to distilled water and diluting to 1 litre. To 100 ml of this solution add 3 ml of 3% hydrogen peroxide (H2O2). Prepare fresh solutions dally and protect from extreme heat or direct sunlight.

6.4 Sample Recovery

  • 6.4.1 Sodium Hydroxide (approximately 1 N). Slowly add 40 g of sodium hydroxide (NaOH) pellets to 800-900 ml of water in a 2-litre beaker with stirring until all pellets are dissolved. Dilute to 1 litre with water and mix well. Store in an airtight storage bottle.

  • 6.4.2 Red Litmus Paper.

6.5 Analysis

  • 6.5.1 Phenol (C6H5OH). Pure white solid. Caution: handle with care.

  • 6.5.2 Sulphuric Acid (sp. gr. 1.84). Concentrated  H2SO4, minimum assay 95%.

  • 6.5.3 Ammonium Hydroxide (sp. gr. 0.90). Concentrated ammonium hydroxide (NH4OH).

  • 6.5.4 Fuming Sulphuric Acid (H2SO4 + free SO3), 15 to 18% by weight, free sulphur  trioxide.

  • 6.5.5 Phenol-Disulphonic Acid Solution. Dissolve 25 g of phenol in 150 ml of concentrated H2SO4 (sp. gr. 1.84) by heating on a steam bath. Cool, add 75 ml of fuming H2SO4 (15-18% SO3) and heat on the steam bath at 100°C (212°F) for 2 hours. Cool and store in a dark glass-stoppered bottle. The solution should be colourless. Note: deteriorates on long standing.

  • 6.5.6 Potassium Nitrate (KNO3). Oven dry at 105-110°C for 2 hours just before preparing the standard solution.

  • 6.5.7 Potassium Nitrate, Stock Standard Solution (1 ml = 1 mg NO2). Dissolve exactly 2.1980 g of dried KNO3 in water and dilute to 1litre in a volumetric flask.

  • 6.5.8 Potassium Nitrate, Working Standard Solution (1 ml = 100 µg NO2). Dilute 10 ml of the stock standard KNO3 solution (6.5.7) to 100 ml with water in a volumetric flask.

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