A novel fatty-acid-based in-tube dispersive liquid–liquid microextraction technique for the rapid determination of nonylphenol and 4-tert-octylphenol in aqueous samples using high-performance liquid chromatography–ultraviolet detection

• Fatty-acid-based in-tube dispersive liquid–liquid microextraction was developed.
• Heptanoic acid was used as either surfactant or extraction solvent by pH adjustment.
• Only acid, alkali, and fatty acid were used to achieve the extraction within 4 min.

In this study, a novel fatty-acid-based in-tube dispersive liquid–liquid microextraction (FA-IT-DLLME) technique is proposed for the first time and is developed as a simple, rapid and eco-friendly sample extraction method for the determination of alkylphenols in aqueous samples using high-performance liquid chromatography–ultraviolet detection (HPLC–UV). In this extraction method, medium-chain saturated fatty acids were investigated as a pH-dependent phase because they acted as either anionic surfactants or neutral extraction solvents based on the acid–base reaction caused solely by the adjustment of the pH of the solution. A specially designed home-made glass extraction tube with a built-in scaled capillary tube was utilized as the phase-separation device for the FA-IT-DLLME to collect and measure the separated extractant phase for analysis. Nonylphenol (NP) and 4-tert-octylphenol (4-tOP) were chosen as model analytes. The parameters influencing the FA-IT-DLLME were thoroughly investigated and optimized. Under the optimal conditions, the detector responses of NP and 4-tOP were linear in the concentration ranges of 5–4000 μg L−1, with correlation coefficients of 0.9990 and 0.9996 for NP and 4-tOP, respectively. The limits of detection based on a signal-to-noise ratio of 3 were 0.7 and 0.5 μg L−1, and the enrichment factors were 195 and 143 for NP and 4-tOP, respectively. The applicability of the developed method was demonstrated for the analysis of alkylphenols in environmental wastewater samples, and the recoveries ranged from 92.9 to 107.1%. The extraction process required less than 4 min and utilized only acids, alkalis, and fatty acids to achieve the extraction. The results demonstrated that the presented FA-IT-DLLME approach is highly cost-effective, simple, rapid and environmentally friendly in its sample preparation.

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