Hexafluoroisopropanol-induced salt-free catanionic surfactant supramolecular solvent for direct immersion single-drop microextraction of sulfonamides and fluoroquinolones in water samples

Abstract

A hexafluoroisopropanol (HFIP)-induced salt-free catanionic surfactant supramolecular solvent (SUPRAS)-based direct immersion single-drop microextraction method was developed and coupled with high-performance liquid chromatography-ultraviolet detection to determine sulfonamides (SAs) and fluoroquinolones (FQs) in lake water samples. Dodecanoic acid and dodecyltrimethylammonium hydroxide were used as the salt-free catanionic surfactant pair for SUPRAS preparation, while HFIP served as the coacervate-inducing agent. Cryo-scanning electron microscopy revealed spherical micellar aggregates in the SUPRAS, which facilitated hydrophobic, hydrogen-bonding, and electrostatic interactions for analyte extraction. A novel holder, fabricated from a gel pen refill protective case, was designed to stably support the high-density SUPRAS droplet (up to 40 μL for 20 min), improving the precision and accuracy of the method. Sulfadiazine, sulfamethazine, norfloxacin, ciprofloxacin, danofloxacin, and enrofloxacin were selected as model analytes. Key factors affecting droplet stability and extraction efficiency were optimized. The method exhibited good analytical performance, with linearity (R2) > 0.9938 and limits of detection of 2.1–3.0 ng mL−1 for SAs and 0.8–1.9 ng mL−1 for FQs. Recoveries for spiked lake water samples were in the range of 81.2–106.3%, with intra- and inter-day relative standard deviations all below 7.2%. AGREEprep greenness assessment revealed that the proposed method achieved the highest score (0.45) among the compared methods, owing to its minimal organic solvent consumption, simple operation, low energy consumption, and low waste generation. Compared with reported methods, the proposed approach is simple, efficient, and environmentally benign, demonstrating strong potential for the trace determination of antibiotics in environmental water samples.