Cetyltrimethylammonium bromide-coated titanate nanotubes for solid-phase extraction of phthalate esters from natural waters prior to high-performance liquid chromatography analysis

As a novel nanomaterial, titanate nanotube has attracted considerable attention recently. However, most of the research work is focused on the preparation of this nanomaterial, and there is lack of information about its application in the fields of environmental monitoring and analytical chemistry. The purpose of our study is to investigate the feasibility of titanate nanotubes as an adsorbent for solid-phase extraction of several phthalate esters. The titanate nanotubes in this study were prepared by alkaline hydrothermal method. The cationic surfactant cetyltrimethylammonium bromide (CTAB)-titanate nanotube system was adopted based on hemimicelles/admicelles formed on the mineral oxide surface. It was shown in the batch experiment that the highest adsorption of phthalate esters onto the CTAB-titania and -titanate nanotube system occurred when the CTAB was varied from 100 to 200 mg g−1 titania or 80 to 300 mg g−1 titanate nanotube separately. According to the fluorescent spectra of a molecular probe, N-phenyl-1-naphthylamine, and the binding constant of solute in CTAB admicelles, the CTAB-titanate nanotube admicelles was more hydrophobic than CTAB-titania admicelles. Consequently, CTAB-titanate nanotube admicelles system was suitable for concentrating phthalates esters in water. An admicelle column was prepared with 100 mg of titanate nanotubes by passing through 100 mg g−1 titanate nanotube of CTAB. And excellent collection yields were obtained for all the analytes when the sample volume was up to 1000 mL. Under the optimal conditions, the detection limits found for di-n-propyl-phthalate, di-n-butyl-phthalate, di-cyclohexyl-phthalate, and di-n-octyl-phthalate were 39, 19, 35 and 20 ng L−1, respectively. The developed method was successfully applied to the analysis of several real water samples and satisfactory recoveries were achieved. All the results indicated the application potential of titanate nanotubes as solid-phase extraction adsorbents to pre-treat water samples.