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This part of ISO 21438 specifies a method for the determination of the time-weighted average mass concentration of hydrogen chloride (HCl) gas and hydrochloric acid mist, hydrogen bromide (HBr) vapour and hydrobromic acid mist and nitric acid (HNO3) vapour and mist in workplace air by collection on an alkali-impregnated quartz fibre filter and analysis by ion chromatography. For mist sampling, the method is applicable to the personal sampling of the inhalable fraction of airborne particles, as defined in ISO 7708, and to static (area) sampling. The analytical method is applicable to the determination of masses of 0,01 mg to 2,5 mg of HCl, HBr and HNO3 per sample. The range of concentrations of HCl, HBr and HNO3 in air for which the measuring procedure is applicable is determined by the sampling method selected by the user. For a 240 l air sample, the working range is approximately 0,04 mg·m-3 to 10 mg·m-3 for HCl, HBr and HNO3. The procedure is intended to differentiate between the acids and their corresponding salts. If both are present in the air, particulate salts are trapped on a pre-filter. Co-sampled particulate matter trapped on the pre-filter and/or deposited on the walls of the sampler may be analysed, if desired. Acids can react with co-sampled particulate matter on the pre-filter, causing interference with the measurement of the acid concentration.