ISO-6840-1982.pdf
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1、International Standard 6840 0 d!i!i 4 INTERNATIONAL ORGANIZATION FOR STANDARDIZATlON.MEWYHAPOLIHAR OPfAHM3AUb4R i-i0 CTAH/lAPTH3Al.WlH.ORGANlSATlON INTERNATIONALE DE NORMALISATION Cationic surface active agents (hydrochlorides and hydrobromides) - Determination of critical micellization concentratio
2、n - Method by measurement of counter ion activity Agents de surface cationiques (chlorhydrates et bromhydrates) - D over a certain concentration range, which is usually very narrow, these curves show a singularity. This phenomenon has been attributed to the formation of oriented aggregates of molecu
3、les, and the concentration at which this change occurs has been termed the “critical micellization con- centration” (c.m.c.1. For a given hydrophobic chain length, the critical micellization concentration is usually higher in the case of ionic surface ac- tive agents than in the case of non-ionic su
4、rface active agents. Apart from the structure of the surface active agent, the temperature and the presence, nature and quantity of metallic salts, organic compounds cause the critical micellization con- centration to vary, and hence the operational conditions likely to influence the result must be
5、clearly stated, i.e. the purity of the product and, as far as possible, its impurities, which may greatly alter the value of measurements of potential (it is very useful to know the organic or mineral nature of these impurities and, if possible, their concentrations). 1 Scope and field of applicatio
6、n This International Standard specifies a method for the deter- mination of the critical micellization concentration of cationic surface active agents (hydrochlorides and hydrobromides) in solution in distilled water or other aqueous systems, by measurement of the counter ion activity using a membra
7、ne electrode. The method is applicable to purified or unpurified cationic sur- face active agents (hydrochlorides and/or hydrobromides), which are soluble in water and which have a Krafft temperature below 60 OC. 3 Definitions 3.1 micelle : See ISO/R 862. 3.2 critical micellization concentration (c.
8、m.c.) : See ISO/R 862. 3.3 Krafft temperature : See ISO/R 862. 4 Principle Potentiometric determination of the chloride or bromide ion ac- tivity of a series of solutions of cationic surface active agents the concentrations of which cover the expected critical micellization concentration. Plotting t
9、he graph of potential as a function of the logarithm of the concentration; the c.m.c. cor- responds to the singularity on this curve. 5 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 6.1 Sodium chloride and sodiu
10、m bromide, standard solu- tions of concentration approximately IO-4 to IO-2 mol/l. 6 Apparatus Ordinary laboratory apparatus and : 6.1 Polycrystalline membrane electrode (sensitive to chlorides (Ag$ + AgCI) or to bromides (AgzS + AgBr). NOTE - It is very important to clean the electrodes according t
11、o the manufacturer s instructions. 2 References IS0 607, Surface active agents and detergents - Methods of sample division. 6.2 Reference electrode : mercury-mercury(l) sulphate with a bridge containing saturated potassium sulphate solution, or a calomel electrode with a double bridge. In the latter
12、 case, the outer bridge shall be filled with saturated potassium nitrate solution. ISOIR 862, Surface active agents - Glossary. NOTE - If the bridge contains sulphate ions, the most concentrated and most dilute surface active agent solutions should be tested with a 1 Copyright International Organiza
13、tion for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/28/2007 07:34:19 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 6840-1982 (El portion of this bridge solution and no precipitation should b
14、e observed. If a precipitate does form, another type of bridge should be used. 6.3 Potentiometer, sensitivity 2 mV (potential of -500 to +500 mV) with a multi-range scale facility. 6.4 Thermostatically controlled water-bath, enabling the temperature of the solution to be controlled to with- in f 0,5
15、 OC. 6.5 Jacketed glass vessel, with an opening suitable for in- troducing the electrodes. 6.6 Magnetic stirrer. 7 Sampling The laboratory sample of cationic surface active agent shall be prepared and stored according to the instructions given in IS0 607. 8 Procedure 8.1 Test portion and preparation
16、 of solutions Weigh, to the nearest 0,l mg, a quantity of the laboratory sam- ple such that 500 ml of a solution about ten times more concen- trated than the c.m.c. is obtained, dissolve in hot water and dilute to 500 ml in a one-mark volumetric flask. Let the concen- tration of this solution be c.
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