Highly sensitive analysis of substituted aniline compounds in water samples by using oxidized multiwalled carbon nanotubes as an in-tube solid-phase microextraction medium

An automated on-line method for the determination of the substituted aniline compounds was developed using in-tube solid-phase microextraction coupling to high-performance liquid chromatography (HPLC). In this work, oxidized multiwalled carbon nanotubes (MWCNTs-COOH) coated on the outer surface of the fused-silica tube and inserted in the polyether ether ketone (PEEK) tubing, which was fixed directly on the six-port injection valve to substitute for the sample loop. The extraction procedure was performed by a constant flow pump frequently driving the sample solution through the PEEK tubing and the analytes were adsorbed onto MWCNTs-COOH materials when the six-port valve set to load position. After extraction, the valve switched to inject position and the extracted analytes were desorbed by mobile phase in dynamic mode. High extraction capacity was achieved for the investigated analytes and great improvement of the limits of detection was obtained in comparison with other methods. The calibration plots were linear (r2 ≥ 0.9949) over the concentration range of 1.04–104 ng mL−1 for 4-nitroaniline, 1.02–102 ng mL−1 for 2-nitroaniline, 1.68–168 ng mL−1 for 2-chloroaniline and 1.09–109 ng mL−1 for 2,4-dichloroaniline. The detection limit ranged from 0.04 ng mL−1 to 0.13 ng mL−1 (at S/N = 3). The possibility of applying the established method to water samples analysis was also studied.