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

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Environmental Science

Background:

• Surfactants form micelles above a critical micelle concentration (CMC) due to their amphiphilic nature.
• Accurate CMC determination is crucial for understanding surfactant behavior in various applications and environmental contexts.

Purpose of the Study:

• To evaluate solid-phase microextraction (SPME) as a method for measuring the CMC of diverse surfactant types.
• To compare SPME-derived CMC values with those obtained via traditional surface tension measurements.
• To investigate the sorption mechanism of surfactants onto polyacrylate-coated SPME fibers.

Main Methods:

• Utilized polyacrylate-coated SPME fibers to measure CMC values for 12 nonionic, anionic, cationic, and zwitterionic surfactants.
• Compared SPME-derived CMC values against those determined by the surface tension method.
• Analyzed fiber-water sorption isotherms to understand the sorption mechanism.

Main Results:

• A distinct break in the concentration relationship between SPME fibers and water was observed at the CMC.
• SPME-derived CMC values agreed within a factor of 3 with surface tension values for 7 out of 12 surfactants.
• Identified limitations for determining CMCs of very hydrophobic cationic surfactants due to fiber cation exchange capacity.

Conclusions:

• SPME is a viable technique for determining surfactant CMCs, offering advantages in analyzing individual compounds within mixtures.
• The method provides insights into surfactant sorption mechanisms on SPME fibers.
• Potential for mixed micelle formation in mixtures can influence CMC measurements.