Trace enrichment of phenolic compounds from aqueous samples by dynamic ion-exchange solid-phase extraction

A novel trace enrichment procedure for ionogenic compounds in environmental aqueous samples, dynamic ion-exchange solid-phase extraction (DIE-SPE), is proposed and evaluated using 15 phenols as model compounds and GC/MS for detection. The procedure is based on the fact that the long-carbon-chain ionic surfactants, such as cetyltrimethylammonium bromide (CTAB), can be steadily adsorbed on the surface of C-18-bonded silica, and the ionized functional groups of the adsorbed surfactant molecules can then act as ion-exchange sites to attract the ionized organic analytes from aqueous samples. At the same time, the bonded silica still remains its function as reversed-phase material. Therefore, the mechanism of DIE-SPE has two aspects, i.e., ion exchange and hydrophobic interaction. Sample pH, the loading amount of surfactant on the solid phase, and volume and matrixes of the sample were studied as the factors that affected the extraction efficiency. When applied to the trace enrichment of ionogenic compounds, DIE-SPE was found to be superior in diverse aspects to traditional reversed-phase bonded material SPE, ion-exchange SPE, carbonaceous or polymer adsorbent SPE: the method had higher extraction efficiency and was less affected by the inorganic ions and humic substance in sample solutions, and the analytes could be easily eluted out from the cartridge. It is proved that DIE-SPE can be used for the trace enrichment of ionogenic compounds from different sources of environmental aqueous samples.