Highly integrated and preloaded liquid-filled stick microextraction with in situ derivatization for determination of sulfonamides in environmental water and milk samples.

Sulfonamides (SAs) are among the most frequently prescribed antibiotic agents, and accurate surveillance of their residues in food products and environmental matrices remains essential. In this study, a preloaded liquid-filled stick microextraction strategy coupled with in situ derivatization (LFSME-ISD) approach was developed for the quantitation of SAs. To construct the extraction device, a hollow polymeric rod was packed with a deep eutectic solvent doped with fluorescamine and capped at one end using polypropylene membrane material. When the device was introduced into 3 mL of sample solution, derivatization occurred concurrently with extraction, promoting the transfer and accumulation of fluorescent products within the deep eutectic solvent phase. After ultrasonic desorption with methanol for 1 min, the derivatives were directly analyzed by liquid chromatography-fluorescence detection. After optimization of the experimental variables, the LFSME-ISD procedure provided excellent linear responses, detection limits of 1.0-2.7 ng/mL, recoveries in pure water of 90.9-105.3%, with relative standard deviation values not exceeding 10.5%. Real-sample fortification at 50 ng/mL gave relative errors of -11.0% to +8.2% in lake water and -14.2% to +12.9% in milk. The preloaded format offers the advantage of combining derivatization-reagent delivery and microextraction within a single downstream operation for sulfonamide determination.