Critical micelle concentration values for different surfactants measured with solid-phase microextraction fibers

The amphiphilic nature of surfactants drives the formation of micelles at the critical micelle concentration (CMC). Solid-phase microextraction (SPME) fibres were used in the present study to measure CMC values of twelve nonionic, anionic, cationic and zwitterionic surfactants. The SPME derived CMC values were compared to values determined using a traditional surface tension method. At the CMC of a surfactant, a break in the relationship between the concentration in SPME fibres and the concentration in water is observed. The CMC values determined with SPME fibres deviated by less than a factor of 3 from values determined with a surface tension method for 7 out of 12 compounds. In addition, the fibre-water sorption isotherms gave information about the sorption mechanism to polyacrylate-coated SPME fibres. A limitation of the SPME method is that CMC for very hydrophobic cationic surfactants cannot be determined when the cation exchange capacity of the SPME fibres is lower than the CMC value. The advantage of the SPME method over other methods is that CMC values of individual compounds in a mixture can be determined with this method. However, CMC values may be affected by the presence of compounds with other chain lengths in the mixture because of possible mixed micelle formation. This article is protected by copyright. All rights reserved.