ISO 6768 pdf download

ISO 6768 pdf download.Ambient air — Determination of mass concentration of nitrogen dioxide — Modified Griess-Saltzman method 1 Scope This International Standard specifies a modified Griess-Saltzman method for the determination of the mass concentration of nitrogen dioxide present in ambient air. The method is applicable to the determination of the mass concentration of nitrogen dioxide present in ambient and confined air within the range 0,003 mg/m 3 to 2 mg/m 3 and for sampling times between 1 0 min and 2 h. Substances present in the air mass under investigation, and thus in the air sample, and known to have an effect on the instrument reading, are given in 7.4. Information on the performance characteristics is given in 8.2. The method is not suitable for personal breathing-zone sampling. The Griess-Saltzman method is suitable for the analytical check of calibration gas mixtures which are used to calibrate chemiluminescence analysers (see ISO 7996). 2 Normative reference The following standard contains provisions which, through reference to this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 6349:1 979, Gas analysis — Preparation of calibration gas mixtures — Permeation method . 3 Principle The nitrogen dioxide present in an air sample is absorbed by passage through an azo-dye-forming reagent within a specified period, resulting in the formation of a pink colour within 1 5 min. The absorbance of the sample solution is then determined at a wavelength between 540 nm and 550 nm using an appropriate spectrophotometer. The corresponding mass concentration of nitrogen dioxide is determined from a calibration graph of absorbance vs. concentration prepared using sodium nitrite solutions of known concentrations. 4 Reagents 4.1 Nitrite-free water. If the water used to prepare the absorption and calibration solutions results in a pink coloration due to the presence of nitrite in the water, prepare nitrite-free water as follows. Add one crystal each of potassium permanganate (KMnO 4 ) and barium hydroxide [Ba(OH) 2 ] to the water and redistill using an all-glass still. 4.2 N -(1-naphthyl)ethylenediamine dihydrochloride, 0,5 g/l stock solution. Dissolve 0,5 g of N -(1 -naphthyl)ethylenediamine dihydrochloride [C 10 H...