Application of solidified floating organic droplet dispersive liquid–liquid microextraction for determination of veterinary antibiotic residues in milk samples with greenness assessment

Antibiotics are the most commonly used veterinary drug category worldwide. The extensive utilization of antibiotics in animal farming is one of the main causes of antibiotic resistance, thus posing a hazard to human health. In the current study, solidification of floating organic droplet dispersive liquid–liquid microextraction (SFO-DLLME) was developed as a green sample preparation step for extracting three widely used veterinary antibiotics; enrofloxacin, ciprofloxacin and oxytetracycline in milk samples present in the Egyptian market. SFO-DLLME was based on using 1-undecanol as a low-toxicity extracting solvent. As several effective parameters are required to be optimized in SFO-DLLME, Box–Behnken experimental design was utilized to obtain the best possible extraction results. The analysis of the analytes was performed through the development of two eco-friendly chromatographic techniques. The first method was based on HPLC-UV where the separation was achieved using C18 column with isocratic elution of mobile phase composed of 0.025 M phosphate buffer (pH 3.2): acetonitrile (85: 15 v/v) and UV detection at 278 nm. The second was UPLC-MS/MS method utilizing BEH shield C18 column acetonitrile: 0.1% formic acid in a ratio of 80:20 (v/v) as mobile phase. The two developed methods were validated it was found that they had high recoveries (88.50 %- 94%), enrichment factors(106.2 %- 112.93 %), low limit of detection (0.077 µg/kg − 29 µg/kg), and satisfactory precision RSD ≤ 2. Different brands of market milk samples were analyzed showing no residues of the studied antibiotics, while enrofloxacin was detected in a concentration of 3.74 µg/kg in raw cow milk samples. Finally, the greenness profile of the developed chromatographic methods was evaluated by the Green Analytical Procedure Index, Analytical GREEnness Metric Approach, and White Analytical Chemistry principles confirming their safety on the environment.