ISO 11564 pdf download.Stationary source emissions – Determination of the mass concentration of nitrogen oxides – Naphthylethylenediamine photometric method
1 Scope
This International Standard specifies a photometric method for the determination of the mass concentration of nitrogen oxides in exhaust gases from ducts or chimneys. NOTE – Nitrogen oxides (NOx) are practically defined as the sum of NO and NO,. The mass concentration of NOx is expressed as the equivalent NO, concentration in milligrams per cubic metre. The method is applicable to the determination of the mass concentration of nitrogen oxides in exhaust gases from combustion processes, processes for surface treatment of metals and from organic chemical reactions, if necessary after removal by washing, in-furnace reduction and/or catalytic denitration, prior to their dispersion into the atmosphere. This International Standard is applicable to the concentration range 5 mg/m3 to 1 O00 mg/m3 as NO, for a sample gas volume of 1 O00 ml. For gas concentrations greater than 1000 mg/m3, the determination of sample gas concentrations up to 5000 rng/m3 can be performed by diluting the sample solution or by taking an aliquot of the sample solution. This International Standard is not applicable to the determination of dinitrogen monoxide (N,O).
2 Principle
Nitrogen oxides in a gas sample are absorbed in an alkaline hydrogen peroxide solution (1,2 mol/l NaOH/ 0,6 % H,OJ in the presence of cupric ions (Cu”), which catalyse the oxidation reaction into nitrite ions. At the above concentrations, nitrate ions are not produced in the absorption solution. Hydrogen peroxide in the absorption solution interferes with the colour development. Therefore, hydrogen peroxide is catalytically decomposed with cupric ions by heating the solution for 30 min in a hot water bath at 80 OC. Nitrite concentration is determined by measuring the absorbance of the coloured solution produced by the reaction with sulfanilamide and naphthylethylenediamine (NEDA) at a wavelength of 545 nm using a photometer. The mass concentration of nitrogen dioxide is obtained by comparison of the absorbance obtained with a calibration graph prepared using a pure sodium nitrite standard solution. The sampling time lies between 5 min and 1 2 min. The time required for the determination is about 60 min.
3 Reagents
Use only reagents of recognized analytical grade and distilled water free of nitrite during the analysis. 3.1 Absorption solution (1,2 mol/l NaOH, 0,6 Yo H,O,, 4,O O h Nazco,, 0,0005 o/o HCOONa) Dissolve 48 g of sodium hydroxide, 40,O g of sodium carbonate and 5 mg sodium formate in about 800 ml of water, add 20 ml of hydrogen peroxide (30 %), and make up to 1 O00 ml with water. NOTE – The absorption solution can be stored in a stoppered vessel in a cool dark place for a week. Shaking promotes the decomposition of hydrogen peroxide. 3.2 Cupric sulfate solution (4 x 1 O-4 mol/l) Dissolve 1 ,O g of cupric sulfate (CuSO, 5H,O) in water in a 1000 ml volumetric flask and make up to the mark. Then dilute 10 ml of this solution in a 100 ml volumetric flask with water and make up to the mark. 3.3 Sulfanilamide/ hydrochloric acid solution (sulfanilamide 0,5 Yo, hydrochloric acid 20 YO) Dissolve 1,0 g of sulfanilamide in about 50 mi water and add 112 mi of hydrochloric acid (37 %) in a 200 ml volumetric flask. Make up to the mark with water. 3.4 Naphthylethylenediamine (NEDA) solution (0,l %) Dissolve 0,l g of NEDA dichloride in 1 O0 ml water. 3.5 Nitrite solution (250 mg/l, expressed as NO; ) Dissolve 375 mg of dried sodium nitrite (NaNO,) and 0,2 g of sodium hydroxide (NaOH) in water in a 1000 ml volumetric flask. Make up to the mark with water and mix well. NOTE – The solution is stable for at least three months if stored in a well-stoppered bottle. 3.6 Dilute nitrite solution (20 mg/l, expressed as NO; )Transfer 40,O ml of the nitrite solution (3.5) to a 500 ml volumetric flask. Make up to the mark with water and mix well; 1 mi of this solution contains 20 pg of NO; . Prepare this solution immediately before use.