ISO INTERNATIONAL STANDARD 11261 First edition 1995-03-01 Soil quality - Determination of total nitrogen -- Modified Kjeldahl method Qualite du sol - Dosage de I'azote total - Méthode de Kjeldahl modifiée ISO Reference number ISO11261:1995(E) ISO11261:1995(E) Foreword iso (the International Organization for Standardization) is a worldwide federation of national standards bodies (Iso member bodies). The work of preparing International Standards is normally carried out through Iso technical committees.Each member body interested in a subject for whichatechnical committeehasbeenestablishedhastherighttobe represented on that committee. International organizations, governmental and non-governmental, in liaison with sO, also take part in the work. isO collaborates closelywith the International Electrotechnical Commission (IEC)onall 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 011261waspreparedbyTechnicalCommittee ISO/TC 190,Soil quality,Subcommittee SC 3,Chemicalmethods and soil characteristics. Annex A of this International Standard is for information only. 1995 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permisston in writing from the publisher. International Organization for Standardization Case Postale 56 CH-1211 Geneve 20 · Switzerland Printed in Switzeriand ii INTERNATIONALSTANDARDISO ISO 11261:1995(E) Soil quality - Determination of total nitrogen Modified Kjeldahl method Scope 3 Principle The method is based on the Kjeldahl-digestion, but ThisInternationalStandardspecifiesamethodforthe determination of the total nitrogen (ammonium-N, titanium dioxide (TiO2) is used as the catalyst instead nitrate-N, nitrite-N and organic N) content of a soil. of selenium. Nitrogen in N-N-tinkages, N-O-linkages and some het- NOTE 1 erocyclics (especially pyridine) is only partially deter- Titanium dioxideis ecotoxicologically less harmfull than selenium. mined. This International Standard is applicable to all types of soils. 4 Reagents All reagents shall be of recognized analytical grade Use water of grade 2 complying with ISO 3696. 4.1 Salicylic acid/sulfuric acid. Normative references Dissolve 25 g of salicylic acid in 1 litre of concentrated sulfuric acid (e = 1,84 g/cm3). The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- 4.2 Potassium sulfate catalyst mixture. cation, the editions indicated were valid. All standards Grind and thoroughly mix 200 g of potassium sulfate are subject to revision,and parties to agreements 6 g of copper(ll) sulfate pentahydrate and 6 g of based on this International Standard are encouraged to investigate the possibility of applying the most re- titanium dioxide, with the crystal structure of anatase. cent editions of the standards indicated below. Members of IEC and ISO maintain registers of cur- 4.3 Sodium thiosulfate pentahydrate. rently valid international Standards Crush the crystals to form a powder that passes Is0 3696:1987, Water for analytical laboratory use through a sieve with an aperture of 0,25 mm. Specification and test methods. 4.4 Sodium hydroxide, c(NaOH) = 10 mol/l. IsO5725:1986,Precisionoftestmethods— Deter- minationofrepeatabilityandreproducibilityfora 4.5 Boric acid solution, p(HgBO3) = 20 g/l. standard test method by inter-laboratory tests. iS0 11464:1994, Soil quality-Pretreatment of sam- 4.6 Mixed indicator. ples for physico-chemical analyses. Dissolve 0,1 g of bromocresol green and 0,02 g of ISO 11465:1993. Soil quality - Determination of dry methyl red in 100 ml of et