4.12  Determination of nitric acid and ammonia absorbed on impregnated filters

Nitric acid, ammonia (and hydrochloric acid) collected on an impregnated filter behind an aerosol filter will not generally reflect the true air concentrations due to physical processes and chemical reactions on the filter, mainly with sulphuric acid. By adding the amount of ions in the aerosol filter and on the impregnated filters, the sum of the concentrations of nitric acid and aerosol nitrate, ammonia and aerosol ammonium, and hydrochloric acid and aerosol chlorides can be determined. Separate determination of the two components can be achieved by use of denuders.

The recommended analytical procedures for nitrate and ammonium after the extraction from the impregnated filters (3.6.1.2) are given in Sections 4.1, 4.3 and 4.4. If the extract containing the nitrates is too alkaline for the method applied, it should be treated with a cation resin as described in Section 3.6. If the sample containing the ammonium extracts is too acid for the methods described in Section 4.4, the solutions may be neutralized by adding sodium hydroxide or buffers with sufficient capacity

4.12.1  Determination of nitrate ions by ion chromatography

The analytical method is described in Section 4.1.

4.12.2  Spectrophotometric determination of nitric acid by reduction to nitrite and reaction with sulphanilic acid

The analytical method is described in Section 4.3.1.

4.12.3  Automatic spectrophotometric determination of nitric acid by reduction to nitrite and reaction with sulphanilic acid

The analytical method is described in Section 4.3.2.

4.12.4  Determination of ammonium ions by ion chromatography

The analytical method is described in Section 4.4.1.

4.12.5  Spectrophotometric determination of ammonia as ammonium by the indophenol blue method

The analytical method is described in Section 4.4.2.

4.12.6  Automatic spectrophotometric determination of ammonia as ammonium by the indophenol blue method

The analytical method is described in Section 4.4.3.


Last revision: November 2001