6557/1 International Standard (ISO INTERNATIONAL ORGANIZATION FOR STANDARDIZATION+MEXAYHAPOAHAR OPTAHM3AUMA NO CTAHAAPTW3AUMMORGANISATION INTERNATIONALE DE NORMALISATION Fruits, vegetables and derived products - Determination of ascorbic acid - Part 1: Reference method Fruits, legumes et produits derives -Détermination de la teneur en acide ascorbique -Partie 1: Methode de reference Firstedition-1986-10-01 UDC635.1/.6:543.426:547.475.2 Ref.No.ISO6557/1-1986(E) 6557/1-1986 Descriptors : agriculturaf products, fruits, vegetables, fruit and vegetable products, chemical analysis, determination of content, ascorbic acid. spectrochemical analysis. OSI Price based on 3 pages Foreword ISo (the International Organization for Standardization) is a worldwide federation of national standardsbodies (lSOmemberbodies).The work ofpreparingInternational Standardsis normally carried out throughISO technical committees.Eachmember body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with Iso, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISo Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO6557/1 was prepared by Technical Committee ISO/TC 34, Agriculturalfoodproducts. and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. InternationalOrganizationforStandardization,1986 Printed in Switzerland ISO6557/1-1986 (E) INTERNATIONALSTANDARD Fruits, vegetables and derived products - Determination of ascorbic acid - Part 1: Reference method 1 Scopeandfieldofapplication 3 Reagents and materials All reagents shall be of recognized analytical grade and the This part of iSo 6557 specifies the reference method, using water used shall be distilled or water of equivalent purity. molecular fluorescence spectrometry,for thedetermination of the combined ascorbic and dehydroascorbic acid content of fruits, vegetables and derived products. 3.1o-Phenylenediamine dihydrochloride (CgHgN2 - 2HCI), 0,2 g/1 solution. Prepare this solution just before use. Principle 3.2 Sodium acetate trihydrate (CHgCOONa-3H20), Transformation of ascorbic acid into dehydroascorbic acid 500 g/I solution. using activated charcoal. 3.3Boric acid/sodiumacetate solution. Reactionofthe dehydroascorbic acid obtainedwith o-phenylenediamine (OPDA)to give a fluorescent compound Dissoive 3 g of boric acid (HBO3) in 100 ml of the sodium accordingtothereaction acetate solution (3.2). Prepare this solution just before use. 3.4 Ascorbic acid,1 g/I standard solution. H NH2 Weigh, to the nearest 0,01 mg, 50 mg of ascorbic acid CH(OH)CH,OH previously dehydrated in a desiccator protected from fight. NH2 Transfer quantitatively to a 50 ml one-mark volumetric flask and make up to the mark with the extraction solution (3.5), just (OPDA) (Dehydroascorbic acid) before use. 3.5 Extraction solution. 3.5.1 Metaphosphoricacid/aceticacid. Transfer 30 g of metaphosphoric acid (HPO3) to a 1 000 ml beaker or conical flask containing 80 ml of glacial acetic acid CH(OH)CH2OH (CH3COOH) and about 500 ml of water. Warm and stir gently H until complete dissolution. (1-Oxo-2,4 H-3-(1,2-dihydroxyethyi) furo [3,4-b] quinoxaline) Allow the solution to cool. Transfer it quantitatively to a 1 000 ml one-mark volumetric flask and make up to the mark with water. or In a control test in the presence of boric acid, formation of the complex HgBO3dehydroascorbic acid to prevent reaction 3.5.2Metaphosphoric acid/methanol. with OPDA. Any fluorescent interference can thus be taken into account in the calculation. Mix3volumes of a 4% (m/m)metaphosphoric acid solution with