Cotton disk-assisted liquid–liquid microextraction with solidification of floating organic drop: HPLC-UV determination of enrofloxacin in swabs for cleaning validation in pharmaceutical manufacturing

Abstract

In this work, a preconcentration approach, cotton disk-assisted liquid–liquid microextraction with solidification of floating organic drop, was developed. A molten extractant (dodecan-1-ol) was placed on the surface of a rotating cotton disc, embedded with a magnetic stirrer bar, for extractant crystallization and retention on the disc. Rotation of the disc in a sample solution on a hot-plate magnetic stirrer (at 65 °C) resulted in extractant melting, tearing and dispersion in sample phase. Dispersion of extractant was achieved without the use of dispersing solvent, as in classical dispersive liquid–liquid microextraction. Cooling of the extraction mixture (−5 °C) with simultaneous rotation of the disc promoted crystallization of extract drop. The solidified floating extract drop was then separated. The preconcentration approach was applied to chromatographic determination of enrofloxacin in swabs for cleaning validation in pharmaceutical manufacturing. The rotating cotton disc ensured efficient dispersion of the extractant in the aqueous sample phase, leading to high analyte recovery between 98 and 105 %. The linear range of analyte detection was 0.6 to 180 mg/L; and the limit of detection (3σ) was 0.2 mg/L.