MODIFIED ON-COLUMN INTERFACE FOR COUPLED HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY GAS-CHROMATOGRAPHY AND ITS APPLICATION TO THE DETERMINATION OF LEVAMISOLE IN MILK

A modified on-column interface is reported for the coupling of high-performance liquid chromatography with gas chromatography, incorporating an adapted, commercially available multidimensional gas chromatography switching system. Novel features include cryogenic analyte focusing, total solvent exclusion from the analytical column and independent carrier gas supplies to the analytical GC column and uncoated pre-column. The instrumentation was used for the determination of the veterinary anthelmintic drug levamisole in milk with analyte detection by both flame ionisation and nitrogen-phosphorus detectors. Detection limits for the assay were 2.2 mug l-1 and 0.4 mug l-1 by flame ionisation and nitrogen-phosphorus detectors, respectively. The assay was applied to a survey of fourteen milk samples from different dairy outlets.