A Green Approach for Profiling Naphthenic Acids in Produced Water Using Deep Eutectic Solvents–Polypropylene-Supported Thin-Film Microextraction and LC-HRMS

High Resolution Image Download MS PowerPoint Slide Produced water (PW) is a byproduct of the oil industry that contains naphthenic acids (NAs), whose chemical complexity requires robust analytical methods to unequivocally identify the analytes and prioritize reducing environmental impacts by reducing generated waste. This study presents the development of a green method combining deep eutectic solvents (DES) with thin-film liquid-phase microextraction (TF-LPME) for the molecular profiling and quantitative determination of 16 NAs in PW samples using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS), namely, a Fourier transform Orbitrap analyzer. Dispersive liquid–liquid microextraction (DLLME) and TF-LPME were compared, and the latter performed better, as DLLME led to the unwanted formation of stable emulsions in real samples. Main extraction conditions, such as desorption solvent, DES volume impregnated on the polypropylene (PP) support, extraction time, DES selection, desorption solvent, volume, and time, were evaluated to determine the optimal conditions for each studied variable. Validation was performed by determining the main method quality parameters. Determination coefficients were all above 0.99, linear ranges from 0.015 μg L –1 to 1.50 μg L –1, and detection and quantification limits ranging from 0.0045 μg L –1 to 0.45 μg L –1 were obtained. The average recovery was 87.9%, with intraday precision ( n = 3) ranging from 8.0 to 16.0% and interday precision ( n = 6) ranging from 10.2 to 16.0%. Method application determined a total concentration of 3.19 ± 0.30 mg L –1 and revealed slightly distinct profiles for the O 2 class with a double bond equivalent (DBE) of 2 in the three analyzed PW samples, identifying 11 homologous series and differences in aromatic compounds. The method was compared with five other literature methods, demonstrating superior sustainability as evaluated by AGREEprep metrics, along with excellent analytical performance and low detection limits suitable for the NA concentration ranges found in real matrices. Thus, the DES-TF-LPME method emerges as an efficient and sustainable alternative for environmental monitoring in the petroleum industry.