Determination of methylbenzoquate in premixes and animal feeds using liquid chromatography with fluorescence detection.

A rapid analytical procedure was developed and tested for routine identification and quantification of methylbenzoquate in feeds by liquid chromatography (LC). The ground feed samples were extracted using methanol-water (80 + 20, v/v) at 65 degrees-70 degrees C in a water bath for premixes and in dichloromethane at 45 degrees C in a water bath for final feeds, respectively. The extract of final feeds was cleaned using solid-phase extraction on silica columns. Both the final feed and premix extracts were analyzed by reversed-phase LC on a NovaPak C18 column (3.9 x 150 mm; 4 microm) with methanol-acetonitrile-water-phosphoric acid (340 + 350 + 308 + 2, v/v) as mobile phase. Fluorescence detection was performed at excitation and emission wavelengths of 265 and 390 nm, respectively. Alternatively, post-column addition of sulfuric acid solution was used to decrease the determination limit. The recovery of methylbenzoquate, in a concentration range of 0.5-10 mg/kg, was 105.0 +/- 7.3%. The limit of quantitation, based on a signal-to-noise ratio of 10:1, was 48 microg/kg. The developed LC method was tested in an interlaboratory study. The interlaboratory repeatibility for both samples ranged from 7.1 to 10.6%; the interlaboratory reproducibility ranged from 11.7 to 15.2%. With the post-column addition of sulfuric acid, the limit of quantification was decreased by a factor of 50. Overall, the developed method is highly selective and can be used in routine analysis.