6840 International Standard (ISO INTERNATIONAL ORGANIZATION FOR STANDARDIZATION+MEKAYHAPOAHAA OPTAHM3ALWH HO CTAHAAPTW3AWW-ORGANISATION INTERNATIONALE DE NORMALISATION ANst lrterrut Doo Sect Cationic surface active agents (hydrochlorides and hydrobromides) - Determination of critical micellization concentration --- Method by measurement of counter ion activity Agents de surface cationiques (chlorhydrates et bromhydrates) - Détermination de la concentration critique pour la formation de micelles -- Methode par mesurage de I'activite de I'ion contraire First edition -- 1982-10-01 UDC 661.185.23 : 543.25 Ref. No. 1SO 6840-1982 (E) Descriptors : surfactants, cationic surfactants, tests, determination, cationic active matter, measurement, ions, critical concentration. Price based on 3 pages sefrom IHS Not for Resale Foreword Iso (the International Organization for Standardization) is a worldwide federation of national 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, governmental : 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. International Standard ISO 6840 was developed by Technical Committee ISO/TC 91 Surface active agents, and was circuliated to the member bodies in November 1981. It has been approved by the member bodies of the following countries : Hungary Australia Poland Austria Italy Romania South Africa, Rep. of Belgium Japan China Spain Korea, Rep. of Switzerland France Mexico USSR Germany, F. R. Netherlands No member body expressed disapproval of the document. International Organization for Standardization, 1982 ? Printed in Switzerland International Organization for Standardization, 1982 Printed in Switzerland Copyright International Organization for Standardization Not for Resale INTERNATIONAL STANDARD ISO 6840-1982 (E) Cationic surface active agents (hydrochlorides and hydrobromides) - Determination of critical micellization concentration --- Method by measurement of counter ion activity O Introduction 3 Definitions Curves showing the variations in the physical properties of 3.1 micelle : See ISO/R 862. aqueous solutions of surface active agents are specific to these products; over a certain concentration range, which is usually 3.2 critical micellization concentration (c.m.c.) : See very narrow, these curves show a singularity. This ISO/R 862. phenomenon has been attributed to the formation of oriented aggregates of molecules, and the concentration at which this change occurs has been termed the "critical micellization con- 3.3 Krafft temperature : See ISO/R 862. centration" (c.m.c.). For a given hydrophobic chain length, the critical micellization 4 Principle concentration is usually higher in the case of ionic surface ac- tive agents than in the case of non-ionic surface active agents. Potentiometric determination of the chloride or bromide ion ac Apart from the structure of the surface active agent, the tivity of a series of solutions of cationic surface active agents temperature and the presence, nature and quantity of metallic the concentrations of which cover the expected critical saits, organic compounds cause the critical micellization con- micellization concentration. Plotting the graph of potential as a centration to vary, and hence the operational conditions likely function of the logarithm of the concentration; the c.m.c. cor- to influence the result must be clearly stated, i.e. the purity of responds to the singularity on this curve. the product and, as far as possible, its impurities, which may greatly alter the value of measurements of potential (it is very usefui to know the organic or mineral nature of these impu