Highly stable magnetic multiwalled carbon nanotube composites for solid-phase extraction of linear alkylbenzene sulfonates in environmental water samples prior to high-performance liquid chromatography analysis

The magnetic multiwalled carbon nanotubes (MMWCNTs) have been successfully prepared using a one-pot chemical coprecipitation method, in which magnetic nanoparticles (MNPs) were deposited onto multiwalled carbon nanotubes (MWCNTs) by in situ high temperature decomposition of the magnetic precursor of iron(III) in ethylene glycol media. A novel procedure for extraction of linear alkylbenzene sulfonates (LAS) as a model compound was thus developed in an off-line extraction system with detection by HPLC. The procedure includes the separation and preconcentration of LAS homologues onto MMWCNTs at pH 7.0 and their subsequent detection after sonication elution, followed by the separation of the MMWCNTs from the aqueous phase by external magnetic field and washing with ultra pure water. With a sample volume of 500 mL and 100 mg MMWCNTs sorbents, an enrichment factor of about 500, and a detection limit of 0.013-0.021 mu g L-1 were obtained within a linear range of 0.5-100 mu g L-1, together with a correlation coefficient of 0.9938-0.9998 for four LAS homologues. A precision of 2.4-5.6% was obtained for six replicate determinations of 50 mu g L-1 LAS. The recoveries of LAS homologues spiked in environmental water samples ranged from 87.3 to 106.3%, demonstrating the utility of the MMWCNTs adsorbents in a series of water samples. Stability testing demonstrated that the MMWCNTs remained 95.0% recovery for the target LAS even after a run of 50 adsorption and desorption cycles, showing their super operational stability. The MMWCNTs are promising adsorbents, suitable for the long-term repetitive sorption/desorption of target compounds in environmental water samples.