Determination of eight fluoroquinolones in groundwater samples with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction prior to high-performance liquid chromatography and fluorescence detection

[Display omitted] ► A novel method by US-IL-DLLME-LC-FD for fluoroquinolones determination. ► Simple, rapid and efficient method for water samples. ► Advantages over conventional methods. ► Low detection limits. An ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction (US-IL-DLLME) procedure was developed for the extraction of eight fluoroquinolones (marbofloxacin, norfloxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, oxolinic acid and nalidixic acid) in groundwater, using high-performance liquid chromatography with fluorescence detection (HPLC-FD). The ultrasound-assisted process was applied to accelerate the formation of the fine cloudy solution using a small volume of disperser solvent (0.4mL of methanol), which increased the extraction efficiency and reduced the equilibrium time. For the DLLME procedure, the IL 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM] [PF6]) and methanol (MeOH) were used as extraction and disperser solvent, respectively. By comparing [C8MIM] [PF6] with 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM] [PF6]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C4MIM] [PF6]) as extraction solvents, it was observed that when using [C8MIM] [PF6] the cloudy solution was formed more readily than when using [C6MIM] [PF6] or [C4MIM] [PF6]. The factors affecting the extraction efficiency, such as the type and volume of ionic liquid, type and volume of disperser solvent, cooling in ice-water, sonication time, centrifuging time, sample pH and ionic strength, were optimised. A slight increase in the recoveries of fluoroquinolones was observed when an ice-water bath extraction step was included in the analytical procedure (85–107%) compared to those obtained without this step (83–96%). Under the optimum conditions, linearity of the method was observed over the range 10–300ngL−1 with correlation coefficient >0.9981. The proposed method has been found to have excellent sensitivity with limit of detection between 0.8 and 13ngL−1 and precision with relative standard deviation values between 4.8 and 9.4% (RSD, n=5). Good enrichment factors (122–205) and recoveries (85–107%) were obtained for the extraction of the target analytes in groundwater samples. This simple and economic method has been successfully applied to analyse real groundwater samples with satisfactory results.