Determination of fifteen phenols in wastewater from petroleum refinery samples using a dispersive liquid—liquid microextraction and liquid chromatography with a photodiode array detector

Abstract

This work proposes for the first time a dispersive liquid-liquid microextraction (DLLME) method for the simultaneous extraction of 15 phenols (including isomers) from refinery wastewater with identification by liquid chromatography coupled to photodiode array detection (LC-PDA). The compounds studied were phenol, cresols, nitrophenols and chlorophenols including the isomers: 2–nitrophenol and 4-nitrophenol; o-cresol, m-cresol and p-cresol; 2,4-dichlorophenol and 2,6-dichlorophenol; 2,4,6-trichlorophenol and 2,4,5-trichlorophenol. Because of the presence of isomers and similar compounds, different mobile phases, comprising several combinations of methanol, acetonitrile and purified water, and different flow rates were tested to provide separation. Also, retention factors, selectivity and resolution were evaluated. For DLLME, volumes of extraction (1-octanol) and disperser (acetone) solvents were optimized by a 22 full factorial design. The optimum conditions involved using the use of 250 μL 1-octanol and 1000 μL of acetone. The limits of quantification were between 2.5 and 10 μg L−1. Analytical recoveries ranged from 69 to 129%, with relative standard deviations (RSD) below 20%. The proposed analytical method was successfully applied to the determination of these compounds in refinery wastewaters. Phenol, o-cresol p + m-cresol and 2,4-dimethylphenol were detected in a concentration range from 15 to 78 μg L−1 and 300–2120 μg L−1 in the treated and raw wastewaters, respectively.