Deep eutectic solvent loaded onto graphene oxide as a novel phase for pipette-tip micro-solid phase extraction of levofloxacin from seawater and body fluid samples

In this research, applicability of an environmentally friendly deep eutectic solvent (DES) for pipette-tip micro-solid phase extraction and preconcentration of levofloxacin prior to its quantification by spectrophotometry at the wavelength of 240 nm is presented. Carvone:thymol (1:1 molar ratio) DES was prepared and coated on graphene oxide and applied as adsorbent. This adsorbent was characterised utilising Fourier transform infrared and field emission scanning electron microscopy, which showed a uniform layer of DES coated on graphene oxide. 5.0 mg of this adsorbent was packed into a 100 & mu;L pipette-tip and was applied to miniaturised pipette-tip solid-phase extraction of levofloxacin. Parameters affecting microextraction including kind and volume of elution solvent, pH, amount of sorbent, sample volume, and number of aspirating/dispensing cycles were investigated and optimised using one-variable-at-a-time procedure, central composite design, and Box-Behnken design response surface methodologies. The developed method required only 5.0 mg of adsorbent and 150 & mu;L of methanol:acetone (2:1) (elution solvent) to achieve a low detection limit of 0.3 & mu;g/L with a linear range of 1-500 & mu;g/L. High enrichment factor of 65.3 with a good precision (RSD & LE; 4.7%) was also achieved. The proposed method was successfully applied to determine levofloxacin in pills, blood, urine and a few seawater samples.