Determination of Tetracyclines in Water by Ethyl Acetate–Ionic Liquid Dispersive Liquid–Liquid Microextraction and High-Performance Liquid Chromatography

Abstract

An ethyl acetate-assisted ionic liquid dispersive liquid–liquid microextraction method was developed for the determination of tetracyclines in water samples with high-performance liquid chromatography using a variable wavelength detector. A mixture of ethyl acetate and 1-butyl-3-methylimidazolium hexafluorophosphate was used to isolate lanthanum(III) chelates of tetracyclines. The addition of ethyl acetate significantly enhanced the extraction efficiencies. Experimental parameters affecting the efficiency such as the identity and volume of ionic liquid, the volume of ethyl acetate, chelating time, centrifuge time, pH, and ionic strength were evaluated. Under the optimum conditions, the calibration curves were linear and the correlation coefficients (r ² ) ranged from 0.9985 to 0.9992 over concentration levels of 0.01–0.50 µg mL⁻¹. The limits of detection (signal-to-noise ratio = 3) of the method ranged from 0.97 to 1.14 ng mL⁻¹, whereas inter- and intra-day relative standard deviations (n = 5) were between 2.4–4.3% and 3.6–6.8%, respectively. This method was used to analyze water samples and recoveries from 62.6% to 109.6% were obtained.

Keywords:

• Dispersive liquid–liquid microextraction
• Ethyl acetate
• High-performance liquid chromatography
• HPLC
• Ionic liquids
• Tetracyclines

ACKNOWLEDGMENT

The authors are grateful to Professor Xuedong Wang of Wenzhou Medical University. The authors are also grateful to the anonymous reviewers for their suggestions and critical comments.

Notes

^a Extraction conditions: water sample volume, 5.00 mL; pH, 7.0; La(III) (0.4 mmol L⁻¹), 50.0 μL; extraction solvent ([BMIM]PF₆) volume, 120 µL; assisted solvent volume, 0.5 mL; chelating time for TCs with La³⁺, 10 min; manual shaking time, 2 min; centrifugation time, 10 min.

^b LDR, linear dynamic range.

^c r ², coefficients of correlation.

^d LOD, limit of detection for S/N = 3.

^e R, recovery.

^f RSD, relative standard deviation (n = 5).

^a RSD, relative standard deviation (n = 5).

DSPM = dispersive solid phase microextraction; SPE = solid phase extraction; IL-EA-DLLME = ethyl acetate-assisted ionic liquid dispersive liquid–liquid microextraction.