Simple HPLC determination of colistin in medicated feeds by pre-column derivatization and fluorescence detection

A simple and sensitive HPLC method was developed for the determination of c olistin antibiotic in feeds employing pre-column derivatization and fluores cence detection. Extraction of colistin in feeds was by sonication and shak ing with 0.1 M HCL Pre-column derivatization was with phthaldialdehyde and 2-mercaptoethanol (ME) in borate buffer (pH 10.5) to obtain a fluorescent d erivative. Elution of the derivative onto an Ultracarb 5 mum ODS column was by using acetonitrile - ultrapure water (75:25). Detection was by spectrof luorimetry at 340 nm (excitation wavelength) and 440 nm (emission wavelengt h). Total elution time was < 20 min. The applicability of the validated met hod was tested by analyzing commercial medicated feeds without any interfer ence from the matrix.