Dihexadecyldimethylammonium hydroxide admicelles on silica for the preconcentration of selected phenols

Admicelle based extractions, where sorbents used are prepared by immobilizing charged surfactants in a bilayer arrangement onto a silica or aluminum oxide surface, have been used for preconcentrating a wide variety of analytes. These analytes have a certain degree of hydrophobicity interacting with the alkyl chains of the surfactant or they are counter-charged interacting electrostatically with the charged polar group of the surfactant. Weakly hydrophobic molecules are more challenging to efficiently extract onto this type of medium. Presented is an admicelle extraction procedure for extracting weak acid phenols. An acid-base reaction takes place between modified surfactants containing hydroxide counter ions and weak acid phenols. The result of this reaction is the production of phenolate ions that remain counter to the cationic surfactant. The acid-base reaction together with the fluid nature of the surfactant phase protects the phenolate ions from being removed by counter ions in natural solutions. High extraction efficiencies result.