Fabrication of dual layered double hydroxide/cobalt oxide sorbent on pencil graphite for solid-phase microextraction and HPLC analysis of environmental pollutants

This study describes the synthesis of Co/Al-LDH through an electrochemical method on a pencil graphite substrate, followed by the partial conversion of Co/Al-LDH to Co₃O₄ via a calcination method on the same substrate. The obtained sorbent served as an extraction phase for the direct solid-phase microextraction (SPME) of environmental pollutants, including chlorophenols and aromatic hydrocarbons, from wastewater samples. The extracted analytes were quantified using high-performance liquid chromatography-ultraviolet detection (HPLC-UV). Under optimal conditions, the linear dynamic range (LDR) extended for each extracted analyte over a concentration range of 1-500 μg L^-1. The coefficients of determination (R²) for the target analytes ranged from 0.9946 to 0.9987. The limits of detection (LODs) were in the range of 0.29-0.69 μg L^-1, while the limits of quantification (LOQs) ranged from 0.96-2.1 μg L^-1. Moreover, spike recovery (SR) for real samples ranged from 90.0 to 113.0 %, indicating the effectiveness of the proposed method. The developed coating showed excellent efficiency and sensitivity for the extraction of chlorophenols and aromatic hydrocarbons from real samples. This work is novel in that it enables the simultaneous extraction of analytes with different polarities using two types of sorbents on the same substrate.