Preparation and further evaluation of l-menthol-based natural deep eutectic solvents as supported liquid membrane for the hollow fiber liquid-phase microextraction of sulfonamides from environmental waters

In this work, the use of a hydrophobic natural deep eutectic solvent (NADES) as supported liquid membrane (SLM) for hollow fiber liquid-phase microextraction (HF-LPME) of sulfonamides is proposed. Different NADES based on l-menthol and naturally occurring organic acids (citric acid, formic acid, acetic acid, decanoic acid, nonanoic acid, lactic acid, valeric acid, isobutyric acid, hexanoic acid, octanoic acid, and 2-methylbutyric acid) were prepared at different molar ratios. Important solvent properties to work as SLM were studied such as stability in the fiber and compatibility with HPLC. Then, the ability of the prepared NADES to extract 8 antibiotics of the family of sulfonamides (SAs) from water by HF-LPME was studied. From them, the combination of formic acid:L-menthol (1:1) was selected as optimum since it provided a better and more balanced extraction of SAs. The optimized HF-LPME procedure was applied to the analysis of an artificial water containing humic acids, tap and river water samples, showing a good clean-up ability for all the tested samples. Calibration curves showed good linearity for all the SAs and samples with linear regression coefficients (r²) greater than 0.992. Relative recoveries ranged from 53 to 121%, with relative standard deviation values between 5 and 21%, depending upon the analyte and type of water sample. The limits of detection of the method varied from 0.63 to 2.85 µg/L for tap water, 0.70 to 3.23 µg/L for the Jarama river and 0.61 to 2.52 µg/L for the Manzanares river. Besides, the proposed method can be considered sustainable, according to AGREEprep tool, and greener than reported methods in the literature based in other microextraction techniques.