ISO INTERNATIONAL STANDARD 6768 Second edition 1998-08-01 Ambient air Determination of mass concentration of nitrogen dioxide Modified Griess-Saltzman method Air ambiantDetermination de la concentration en masse de dioxyde d'azoteMéthode de Griess-Saltzman modifiée ISO Referencenumber ISO 6768:1998(E) yIHSunder Not for Resale ISO 6768:1998(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (isO memberbodies).TheworkofpreparingInternationalStandardsisnormallycarriedoutthroughISOtechnical committees. Each member body interested in a subject for which a technical committee has been established has liaison with IsO, also take part in the work. IsO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 6768 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 3, Ambient atmospheres. This second edition cancels and replaces the first edition (isO 6768:1985), which has been technically revised. Annex A of this International Standard is for information only. @ISO1998 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic nternationalOrganizationforStandardization Casepostale56·CH-1211Geneve20·Switzerland Internet [email protected] Printed in Switzerland ational Organization for Standardizatior ISO 6768:1998(E) INTERNATIONAL STANDARD ISO Ambient air Determination of mass concentration of nitrogen dioxide Modified Griess-Saltzman method 1 Scope concentrationofnitrogendioxidepresentinambientair. The method is applicable to the determination of the mass concentration of nitrogen dioxide present in ambient and 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 6349:1979, Gas analysis-Preparation of calibration gas mixtures -Permeation method. 3 Principle specified period, resulting in the formation of a pink colour within 15 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 4 Reagents During the analysis, use only reagents of recognized analytical grade and only nitrite-free water (4.1).