Separation of unsaturated C18 fatty acids using perfluorinated-micellar electrokinetic chromatography: I. Optimization and separation process.

Ammonium perfluorooctanoate (APFOA) was used as a surfactant for the separation of free unsaturated C18 fatty acids by micellar electrokinetic chromatography. A simple background electrolyte of 50 mM APFOA water/methanol (90:10, v/v) at pH = 10 enabled the repeatable separation of oleic acid, elaidic acid, linoleic acid, and alpha-linolenic acid in less than 20 min. Separation conditions were optimized regarding various parameters (organic solvent, counterion, APFOA concentration, and pH). Because the repulsive interactions between fluorocarbon chains and hydrogenated chains are known to lead to segregation and phase separation, the choice of perfluorinated micelles to separate such perhydrogenated long-chain acids could appear astonishing. Therefore, the critical micelle concentration, the charge density, and the mobility of the micelles have been determined, resulting in a first description of the separation process.