Determination of Multi-Residue of Brominated Phenols in Water, Sawdust Powder, and Fish Meal Samples by Preconcentration with Hydrophobic Menthol-Based Natural Deep Eutectic Solvent and HPLC-DAD

Abstract

In this work, a menthol-based natural deep eutectic solvent (NADES) was prepared and applied for the liquid–liquid microextraction (LLME) of five brominated phenols (BPs) (2-bromophenol, 4-bromophenol, 2,6-dibromophenol, 2,4-dibromophenol, and 2,4,6-tribromophenol) from river and lake water, sawdust powder, and fish meal samples, with further determination by HPLC-DAD. NADES were characterized by using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Proton Nuclear Magnetic Resonance (1H NMR). Method optimization was performed using a 24 factorial design and Doehlert design combined with the Derringer–Suich desirability function and response surface methodology, using the NADES produced with menthol and acetic acid. Optimal extraction conditions were achieved at a pH of 3.92, with 11.56% (w/v) NaCl, a vortex-assisted extraction time of 108 s, and 100 μL of NADES. Analytical performance parameters were established, yielding enrichment factors ranging from 90.2 to 120.8 and low limits of quantification (LOQs) between 0.49 and 1.47 μg L–1. Intraday (n= 5) and intermediate (n= 5) precision, expressed as relative standard deviation (%RSD), ranged from 1.14% to 5.11% at concentrations of 5.0, 25.0, and 75.0 μg L–1. The method was successfully applied to the analysis of BPs in river and lake water samples, as well as in sawdust powder and fish meal, using external calibration, and High-Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS) was used to confirm the presence of 2-bromophenol, 4-bromophenol, and 2,6-dibromophenol in fish meal samples. The proposed method offers notable advantages, including high sensitivity, operational simplicity, and adherence to green chemistry principles due to the use of environmentally friendly solvents.