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

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 (0.4 mL 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 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 10-300 ng L-1 with correlation coefficient > 0.9981. The proposed method has been found to have excellent sensitivity with limit of detection between 0.8 and 13 ng L-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. (C) 2012 Elsevier B.V. All rights reserved.