Modified dispersive liquid-liquid microextraction followed by high-performance liquid chromatography for the determination of clenbuterol in swine urine

A modified dispersive liquid liquid microextraction (DLLME) technique combined with an HPLC-UV procedure was developed for the extraction and determination of clenbuterol in swine urine. The modification involved the selection of methyl tert-butyl ether (MTBE) as the dispersive solvent, which had a low solubility in aqueous samples, playing the part of dispersion with the help of violent shaking. MTBE improved the partition of clenbuterol into the extractant, and helped the formation of phase separation. Various factors affecting the extraction efficiency including selection of the organic extractant and the dispersive solvent, the volume of extractant and dispersive solvent, salt concentration, NaOH concentration and centrifugation time were evaluated and optimised. Under the optimal conditions, precision, linearity (correlation coefficient, r(2)=0.996 over the concentration range of 10-1000 ng ml(-1)), detection limit (2.4 ng ml(-1)) and enrichment factor of 55 were obtained. The modification to the DLLME made it suitable for analytes with pronounced solubility, especially when the compounds are highly polar and thus more difficult to extract effectively by DLLME. The procedure was suitable for the fast screening of clenbuterol residue in swine urine.