Analytical procedure for the determination of tetracyclines in medicated feedingstuffs by liquid chromatography-mass spectrometry

Introduction: The article presents a rapid and simple analytical procedure for determination of four tetracyclines (oxytetracycline, tetracycline, chlortetracycline, and doxycycline) in animal medicated feedingstuffs. Material and Methods: Two-gramme samples were extracted by a Na2EDTA-McIlvaine buffer (pH 4)/methanol mixtures (40/60, v/v). The determination was achieved by liquid chromatography using a Zorbax Eclipse XDB C18 analytical column with mass spectrometer detection (LC-MS). Results: Recoveries of the antibiotics from spiked feed samples ranged from 78.2% to 113.5%. The LOD and LOQ for tetracyclines in feeds ranged from 2.8 to 4.2 and from 4.3 to 5.7 mg/kg, respectively. Conclusion: The method was successfully validated and proved to be efficient, precise, and useful for quantification of tetracyclines in medicated feedingstuffs.

Ion Suppression Study for Tetracyclines in Feed

Ion suppression in analysis of tetracyclines in feed was studied. The conventional analysis consists of a liquid extraction followed by a clean-up step using solid phase extraction (SPE) technique and analysis of the tetracyclines by liquid chromatography and mass spectrometric detection. Various strategies for extraction and cleanup were tested in the present work, and the effectiveness to decrease the ion suppression on the MS/MS signals was evaluated. Four sample treatment methods were tested with five different feed samples. Extraction solvents tested were McIlvaine buffer and a mixture of McIlvaine buffer dichloromethane (3 : 1). SPE cartridges for cleanup were Oasis HLB, Oasis MCX, and Oasis MAX. The effectiveness of the methods was evaluated in terms of decreasing the ion suppression effect but also of decreasing the variability of ion suppression between samples. The method that provided the most satisfactory results involved a clean-up step based on SPE using mixed-mode cation exchange cartridges (Oasis MCX).

Heat Resistance of Bacillus subtilis in Buffer and Foods of Different pH

Heat resistance of a strain of Bacillus subtilis was measured in homogenized canned mushrooms, peas, lentils, meat balls, and tomato; in rehydrated potato purée; and in buffer at selected pH values, to detect any influence of pH and/or-menstruum upon heat resistance. Heat resistance experiments were carried out under continuous monitoring of pH. Dt = 1 min in buffer at pH 4.2, 5.2, 6.1, and 7.1 was obtained at 89.1, 97.3, 104.4, and 107.1°C, respectively. The effect of pH was lower the higher the temperature of treatment. The z values ranged from 6.4 at pH 7.1 to 10.3 at pH 4.2. Heat resistance was mainly dependent on pH of food, but an influence of the food itself was also observed. The pH influenced z value in McIlvaine buffer but not in foods. Prediction of heat resistance values in foods from data obtained in buffer at the same pH is unadvisable as it may lead to errors. These errors will become greater in acid foods the higher the temperature of treatment.

Polarographic Study of the Streaming Maximum of Nitrobenzene in Mcilvaine Buffer

The polarographic maximum of nitrobenzene (first reduction step) is studied at pH 2.2, 5.3 and 7.8. The nature of the maximum is pH dependent and it changes from positive first kind (at pH = 2.2) to negative maximum of the first kind (at pH 5.3, 7.8). At higher flow-rates, compound maxima occur and clear reversal potentials are located where maximum of first kind is transformed into the second kind and vice versa. The morphology of current-time curves has been examined critically in the light of streaming patterns, electrode circuitry, flow-rates and exponents of t at varying intervals during the drop life