Objective of research: Development of methods for the determination of fenbendazole and its metabolites in milk by liquid chromatography coupled with tandem mass spectrometry. Materials and methods: Fenbendazole was administered orally to five cows. Samples of milk were taken on 1, 3, 5 and 10 days of drug application. The research method includes a description of reagents, plates and equipment; mass-spectrometric conditions for analysis of fenbendazole and its metabolites; preparation of the equipment to operation; preparation of eluent solution; preparation of the chromatograph to analysis; determination of chromatographic parameters of standard drug samples; preparation of milk samples to analysis; establishment of parameters of extracts’ chromatography; procedure of calibration of fenbendazole and its metabolites in eluent. Results and discussion: When studying the pharmacokinetics of fenbendazole and its metabolites (sulfone and sulfoxide) in milk, it was found that the maximal concentrations were determined 24 h after drug administration and were 22,6 ng/ml for fenbendazole sulfone, 34,0 ng/ml for fenbendazole sulfoxide and 19,7 ng/ml for fenbendazole. 10 days after treatment, the concentrations of fenbendazole and its metabolites in milk did not exceed permitted values.

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The paper deals with the results of research and development of the electromagnet current control unit for the case when only two outputs without specifying the polarity of the source connection may be available from a circuit with a series of DC voltage sources and electromagnet winding. Theoretical results have been verified by modelling in Matlab-Simulink environment as well as by testing the starter of the contactor air switch.

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