HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF AMOXICILLIN IN MICROLITER VOLUMES OF CHINCHILLA MIDDLE-EAR EFFUSION AND PLASMA

A reversed-phase high-performance liquid chromatographic procedure was developed to analyze 75 mu-l volumes of chinchilla middle ear effusion and plasma for amoxicillin. The small sample volumes were dictated by the chinchilla model we use to study otitis media and our need to collect multiple samples over an 8-h dosing interval. Amoxicillin was separated on an octylsilane column using methanol-10 mM sodium dihydrogen phosphate-acetonitrile, (88:10:2, v/v), pH 3. Amoxicillin and the internal standard were detected at 230 nm. Middle ear effusion and plasma samples were precipitated with perchloric acid and neutralized prior to injecting 6-mu-l onto the column. The limit of quantitation in plasma and middle ear effusion was 0.5 mu-g/ml (coefficient of variation 14.8% and 18.2%, respectively), and 99% of amoxicillin was recovered.