Determination of bitertanol residues in strawberries by liquid chromatography with fluorescence detection and confirmation by gas chromatography/mass spectrometry.

A simple and rapid method was developed for determining bitertanol residues in strawberries. Bitertanol was extracted from samples with ethyl acetate. Bitertanol acetate was added prior to extraction as a surrogate standard. The ethyl acetate extract was cleaned up by passing through tandem solid-phase extraction columns consisting of anion-exchange (SAX) and aminopropyl (NH2) bonded silica. The eluate was evaporated to dryness and reconstituted with methanol. Bitertanol residues were determined by liquid chromatography with fluorescence detection. Recoveries at 4 fortified levels (0.05, 0.25, 0.5, and 1.0 microgram/g), calculated by the internal standard method, ranged from 92.1 to 99.1%, with coefficients of variation ranging from 0.3 to 4.0%. The detection limit was 0.01 microgram/g. Of 25 commercial strawberry samples analyzed for bitertanol residues, 5 contained bitertanol residues at concentrations ranging from 0.02 to 0.51 microgram/g. Positive samples were confirmed by gas chromatography/mass spectrometry with mass-selective detection (m/z 170 and 168).