1971 Volume 44 Issue 10 Pages 2630-2634
Gel filtration of an aqueous solution of sodium dodecylsulfate (SDS) was carried out using Sephadex G-50 as a gel column, and the overall elution rate (Rf) of SDS was measured. The value of Rf was found to be independent of the concentration C of SDS below a certain point, above which it increased with increasing C. A sharp break point observed coincided with the critical micelle concentration (CMC) of SDS. The intermicellar concentration of SDS was estimated from the shape of the elution curve for the solutions beyond CMC, and shown independent of the total concentration C. The value of Rf for the micelle was further determined by direct measurement. The value was found to increase slightly with C above CMC, becoming practically constant above about 1.4×10−2 mol/l. It was concluded from the results that the size of the micelle also increase with the concentration above CMC. Theoretical equations were derived for the relation between Rf and C below and above CMC. Observed Rf vs. C relation fitted the equations satisfactorily, from which CMC was calculated. A rapid equilibrium between micelles and monomer ions and the independence of intermicellar concentration on C were also confirmed.
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