Effect of surfactant loading on the extraction properties of C-18 bonded silica used for solid-phase extraction of phenols

A solid phase extraction (SPE) system has been modified with cationic surfactants and evaluated for extraction and preconcentration of trace phenolic compounds contaminants in water at low ppb concentrations. Cationic surfactants such as cetyl trimethyl ammonium bromide (CTAB) has been steadily adsorbed on the surface of C-18 bonded silica, and the ionized functional group of the surfactant can then act as an ion-exchange site to attract the ionized phenolic compounds from water samples. The method includes enrichment of the phenolic compounds by the surfactant-loaded solid phase extraction system, followed by elution of the analyte with methylene chloride and derivatization of the phenolic compounds with acetic anhydride. Thirty-two phenolic analytes were identified and quantitatively determined by this method; identification and quantification of the compounds is performed with GC/FID using 2-bromophenol as internal standard. SPME analysis with this method was linear over 3-6 orders of magnitude, with linear correlation coefficient (R(2)) greater than 0.96. Experimentally determined FID detection limits ranged from similar to 30 ppt for methyl-substituted phenols to similar to 0.1ppb for phenol and chlorosubstituted phenols. We tested the influence of sample pH, the loading amount of surfactant on the solid phase, and the volume and matrixes of the sample were studied. Absolute recoveries fi om pure water spiked with 0.2 ppb phenolic compounds were 96 - 103%. The method has been applied to analysis of various natural waters, including ground water, lake water, seawater, and wastewater. Recoveries from ground water, lake water, seawater, and wastewater were 92 - 106%, 75 - 93%, 87 - 103%, 86 - 99%, respectively. Therefore, the new technique proved to be an excellent tool for trace enrichments of phenolic compounds at low ppb concentration of these analytes, from different natural water samples.