RAPID ANALYSIS OF ANIMAL DRUG RESIDUES BY MICROCOLUMN SOLID-PHASE EXTRACTION AND THERMAL-DESORPTION ION-TRAP MASS-SPECTROMETRY

A new approach was developed for the rapid and quantitative determinat ion of an anthelmintic drug, phenothiazine, in milk. The technique inv olves a simple extraction procedure using a C-18 microcolumn disc, fol lowed by thermal desorption of the analyte from the disc directly into an ion trap mass spectrometer. The compounds are selectively ionized by isobutane chemical ionization and detected by tandem mass spectrome try. With this approach, 10 ppb detection limits were achieved with as little as 100 mu L milk and only 10 min of analysis time. This approa ch was used to analyze samples of milk taken from a cow administered a one-time therapeutic dose of phenothiazine. The target compound could be detected at 56 h post-dosage, corresponding to a concentration of 30 ppb.