2913 NTERNATIONAL STANDARD (ISO INTERNATIONAL ORGANIZATION FOR STANDARDIZATION -MEKIyHAPOAHA OPrAHW3ALIWS IO CTAHIAPTW3ALIWW.ORGANISATION INTERNATIONALE DE NORMALISATION Wool - Colorimetric determination of cystine plus cysteine in hydrolysates Laine - Détermination colorimetrique de la cystine et de la cystéine dans les hydrolysats First edition -- 1975-05-15 ISO 2913-1975 (E) Ref. No. ISO 2913-1975 (E) UDC 677.31 : 677.01 Descriptors : textiles, wool, chemical analysis, determination of content, amino acids, cystine, colorimetric analysis, cysteine. Price based on 4 pages Copyright InternationalOrganizationfor Standardization Not for Resale ted without license from IHS FOREWORD ISO (the International Organization for Standardization) is a worldwide federation of national standards institutes (isO Member Bodies). The work of developing International Standards is carried out through ISO Technical Committees. Every Member Body interested in a subject for which a Technical Committee has been set up has the right to be represented on that Committee. International organizations, 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. International Standard 1 ISO2913 3wasdrawnup by Technical Committee ISO/TC 38, Textiles, and circulated to the Member Bodies in November 1972. It has been approved by the Member Bodies of the following countries : Germany Australia Portugal Belgium Hungary Romania Brazil India South Africa, Rep. of Bulgaria Iran Sweden Canada Switzerland Israel Czechoslovakia Japan Thailand Denmark Netherlands Turkey Norway Egypt, Arab Rep. of United Kingdom Finland Poland U.S.A. The Member Body of the following country expressed disapproval of the document on technical grounds : France @ International Organization for Standardization, 1975 5 Printed in Switzerland tedwithout license fromIHS Not for Resale ISO 2913-1975 (E) INTERNATIONAL STANDARD Wool - Colorimetric determination of cystine plus cysteine in hydrolysates 0 INTRODUCTION 2 PRINCIPLE Cystine is the most important amino acid in wool. Its Hydrolysis of the wool in aqueous sulphuric acid. Reaction disulphide group is very reactive and is attacked by a wide of the buffered hydrolysate with sodium disulphite and range of reagents used in wool processing. While acid dodecatungstophosphoric acid, resulting in the treatments affect the cystine content only slightly, alkalis, development of a blue coloration, the intensity of which is oxidizing and reducing agents, steam and exposure to light proportional to the concentration of cystine plus cysteine and heat cause it to decrease. Since fibre damage is often in the hydrolysate. Colorimetric determination of the associated with a decrease in cystine content, a method for optical density of the blue solution and calculation of the its determination is useful for the control and diagnosis of sum of cystineplus cysteine. degradation caused by certain agents. NOTE -- The following qualitative test, applicable to undyed wool or a hydrolysate (with dyed wool the hydrolysate must be used), The present method is based on the Folin-Shinohara can be used to determine if the wool to be tested contains a method for the estimation of cystine in acid hydrolysates significantly higher than normal amount of cysteine. of proteins but it should be noted that the cystine content a) Undyed wool : immerse the sample in 1% sodium of intact wool is not necessarily the same as that of its pentacyanonitrosyiferrate sotution until thoroughly wetted, hydrolysate. The method is simple to carry out, requires remove, dry between filter papers and expose to ammonia little special apparatus and is suitable for use in industrial fumes. A red-violet coloration indicates cysteine residues. laboratories. b) Hydrolysate : Transfer 2 to 3 ml of hydrolysate to a test-tube, add 2 or 3 drops of sodium pentacyanonitrosylferrate