ISO INTERNATIONAL STANDARD 6491 Second edition 1998-12-15 Animal feeding stuffs Determination of phosphorus content Spectrometric method Aliments des animaux - Détermination de la teneur en phosphore- Méthode spectrométrique ISO Reference number ISO 6491:1998(E) ISO 6491:1998(E) Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies (isO 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 6491 was prepared by Technical Committee ISO/TC 34, Agricultural food products, Subcommittee SC 10, Animal feeding stuffs. This second edition replaces the first edition (isO 6491:1980), which has been technically revised. Annexes A and B of this International Standard are 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 Case postale 56·CH-1211Geneve 20·Switzerland Internet [email protected] Printed in Switzerland ii ISO6491:1998(E) INTERNATIONAL STANDARD @ ISO Animal feeding stuffs Determination of phosphorus content Spectrometric method 1 Scope This International Standard specifies a spectrometric method for the determination of the phosphorus content of animal feeding stuffs. The method is applicable to animal feeding stuffs with a phosphorus content less than 50 g/kg. It is particularly 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were 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 editions of the standards indicated below. Members of IEC and Iso maintain registers of currently valid International Standards. IsO 3696:1987, Water for analytical laboratory use -Specification and test methods. IsO 6498:1998, Animal feeding stuffs Preparation of test samples. 3 Principle Atestportionofthesampleiseitherashedwithlimeandheatedwithacid(inthecaseoforganicfeedingstuffs)or wet oxidized with a mixture of sulfuric and nitric acids (in the case of mineral compounds and liquid feeding stuffs) solution obtained is measured at a wavelength of 430 nm. 4 Reagents Use only reagents of recognized analytical grade. 4.1 Water, complying to at least grade 3 in accordance with ISO 3696. 4.2 Calcium carbonate. 4.3 Hydrochloric acid, c(HCl) ~ 6 mol/l. 4.4 Nitric acid, c(HNO3) ~ 1 mol/l. 4.5 Nitric acid, c(HNO3) = 14 mol/l, p(HNO3) ~ 1,40 g/ml.