Determination of dephosphate bromofenofos in milk by liquid chromatography with electrochemical detection.

A sensitive, specific method for the determination of dephosphate bromofenofos (DBFF) in milk by liquid chromatography (LC) with electrochemical detection is described. DBFF, the only metabolite of bromofenofos (BFF, a fasciolicide), was extracted from milk by liquid-liquid partition with acetone, acetonitrile, and dichloromethane and purified by using a C18 cartridge. The compound was separated from the matrix peaks by reversed-phase LC and detected by dual-electrode coulometric detection on a Kaseisorb LC ODS-300-5 (250 x 4.6 mm id, 5 microns) column. The mobile phase was acetonitrile-0.05M potassium dihydrogen phosphate (55 + 45, v/v) at pH 3.0. The flow rate was 1 mL/min at 40 degrees C. The applied potentials of detectors 1 and 2 were maintained at 0.30 and 0.45 V, respectively. Average recoveries (n = 5) of DBFF from milk spiked at 1 and 10 ng/mL were 73.1 and 82.7%, respectively; and coefficients of variation were 8.4 and 2.8%, respectively. The detection limit of DBFF in milk was 0.2 ng/mL. Fifty-nine raw and 181 commercial milks were analyzed. DBFF was detected in 4 raw milks (0.2-1.5 ng/mL; average, 0.6 ng/mL) and in 3 normal liquid commercial milks (0.3-0.7 ng/mL; average, 0.5 ng/mL). The identity of DBFF from milk was confirmed by gas chromatography/mass spectrometry.