Using cobalt/chromium layered double hydroxide nano-sheets as a novel packed in-tube solid phase microextraction sorbent for facile extraction of acidic pesticides from water samples

Abstract

In this work, a “packed in-tube” configuration has been developed for packed in-tube solid phase microextraction followed by high performance liquid chromatography. Cobalt/chromium-layered double hydroxide (Co/Cr (NO₃⁻)-LDH) nano-sheets were synthesized by a simple coprecipitation method and were employed as a packed in-tube solid phase microextraction sorbent. The developed method and the synthesized sorbent were applied for the extraction and preconcentration of two different groups of acidic pesticides with different charges including an acidic herbicide (haloxyfop, anionic form) and insecticide (hexaflumuron, neutral form) from aqueous solutions. The extraction ability of the developed method was investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). Characterization of the LDH powder using XRD and SEM images showed that it consists of a large number of inter-crossed and curved nano-sheets with plate-like morphology. Several important factors affecting the extraction efficiency such as the pH of the sample solution, the extraction/desorption time, the flow rate of the sample solution and type of desorption solvent were optimized. Under the optimized conditions, good intra- and inter-assay precisions (RSD%, n = 5) in the range of 3.3–3.9% and 4.2–4.9%, respectively, were obtained. Also, the limits of detection were in the range of 0.05–0.08 μg L⁻¹. This method showed good linearity for the pesticides in the range of 0.1–500 μg L⁻¹ with coefficients of determination better than 0.9984 in water samples. This validated method was successfully applied in the analysis of haloxyfop and hexaflumuron in some water samples. Finally, it can be said that this method has the potential to be a general and reliable alternative for the analysis of acidic pesticides in anionic and neutral forms in real water matrices.