Determination of bithionol, bromophen, nitroxynil, oxyclozanide, and tribromsalan in milk with liquid chromatography coupled with tandem mass spectrometry.

LC/MS/MS was developed to determine the residues of bithionol (BTN), bromofen (BMF), nitroxynil (NTX), oxyclozanide (OCZ), and tribromsalan (TBS) in milk. Samples were extracted with ethyl acetate and cleaned up by liquid-liquid separation with acetonitrile and n-hexane. The compounds were determined by RP-LC using a C18 column with 0.1% formic acid-methanol. Mass spectral acquisition was performed in the negative mode by applying selected-reaction monitoring. The method was validated in milk spiked with these compounds at 5-600 microg/kg; average recoveries were in the range 83.8-97.1%, with RSD values of 1.4-8.0%. The interassay RSDs were less than 11%. The LODs of these compounds in milk were 0.1 microg/kg. The method was applied to 24 raw milk samples. The concentration of these compounds in all samples was lower than the Japanese maximum residue limits. The method is rapid, sensitive, and specific for monitoring residues of BTN, BMF, NTX, OCZ, and TBS in milk.

[Concentration in plasma and excretion in milk of lactating cows after oral administration of tribromsalan, oxyclozanide and bromofenofos].

The fasciolicides tribromsalan (TBS), oxyclozanide (OCZ) and bromofenofos (BFF) were orally administered to three lactating cows. The concentrations of TBS, OCZ and the BFF metabolite dephosphate bromofenofos (DBFF) in plasma, and the excretion of these compounds in milk were determined by high-performance liquid chromatography. In plasma, the concentrations of TBS, OCZ and DBFF reached maximum at about 1.0 day and the compounds remained detectable until 5.7, 7.4 and 15.1 days after administration, respectively. The detection limits of these compounds in plasma were 10, 2 and 2 ppb, respectively. In milk, the concentrations of TBS, OCZ and DBFF reached maximum at about 24 hours and the compounds remained detectable until 30-47, 30-47 and 78-119 hours after administration, respectively. The detection limits of these compounds in milk were 5.1 and 1 ppb, respectively. The residence times of TBS and BFF were very close to the withdrawal times of the fasciolicides.

Spectrophotometric multicomponent resolution of a veterinary formulation containing oxfendazole and oxyclozanide by multivariate calibration-prediction techniques.

Four multivariate calibration-prediction techniques, classical least-squares, inverse least-squares, principal component regression and partial least-squares regression were applied to the spectrophotometric multicomponent analysis of a veterinary formulation containing oxfendazole (OXF) and oxyclozanide (OXC) without any separation step. The multivariate calibrations were constructed by measuring the absorbance values at 14 points in the 285-350 nm wavelength range and by using the training set of standard mixtures containing OXF and OXC in the different compositions. The validity of building multivariate calibrations was checked by using the synthetic mixtures of both drugs. The multivariate calibration models were successfully applied to the spectrophotometric determination of OXF and OXC in laboratory prepared mixtures and a veterinary formulation. The results obtained were statistically compared with each other.

LC assay method for oxfendazole and oxyclozanide in pharmaceutical preparation.

A method has been developed for the simultaneous determination of oxfendazole and oxyclozanide in a pharmaceutical preparation. The method involves reversed phase chromatography with isocratic elution of the mobile phase and detection at 300 nm. The range of quantification for oxfendazole and oxyclozanide was found to be 2-7 microg ml(-1) and 3-10 microg ml(-1), respectively. The validity of the method was evaluated in terms of linear regression analysis, precision, specificity and accuracy.

Simultaneous determination of five fasciolicides in milk by liquid chromatography with electrochemical detection.

A sensitive and specific method is described for determination of 5 fasciolicides in milk. The drugs are used to control liver flukes in cattle. The milk sample was homogenized with acetone and acetonitrile, sonicated, and centrifuged. The supernatant was extracted with dichloromethane. The extract was evaporated to dryness, dissolved in 1% sodium hydrogen carbonate, and purified on a C18 cartridge. The 5 drugs were separated from the matrix by reversed-phase liquid chromatography (LC) and determined by dual-electrode coulometric detection on a Kaseisorb LC ODS-300-5 column. The mobile phase was acetonitrile-0.05M potassium dihydrogen phosphate (55 + 45) at pH 3.0. The flow rate was 1 mL/min at 40 degrees C. The applied potentials of detectors 1 and 2 were set at 0.20 and 0.55 V, respectively. The average recovery of the drugs added to milk at 0.01 and 0.1 micrograms/mL was 89.6%, and the coefficient of variation was 4.7%. The detection limits of the drugs in milk were 4-20 ng/mL. The method is used to monitor commercial milk samples and to determine the residual levels of these drugs in milk from cows treated with a fasciolicide.