Development of strategies to improve extraction, clean-up, and detection of tetracycline antibiotics from various soil types
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An optimized extraction and clean-up method for the analysis of tetracycline antibiotics in soil is presented in this dissertation. Soil extraction using different solvents was investigated, but the use of a 50/50 (v/v) methanol/acetate buffer (pH 8) solvent mixture in pressurized liquid extraction (PLE) system proved to give the best extraction efficiency and reproducibility. The effect of soil composition on the PLE extraction efficiency was also examined, and results indicated that recovery data for one soil is not necessarily consistent with other soil types containing different compositions of clay and organic matter content. The percent recoveries of the optimized PLE method varied between the soils and ranged from 22-99%, depending on soil type, and more specifically clay content. A field study was conducted to determine the persistence of oxytetracycline in the environment, and it was found that residues persist for up to three years in the soil. In addition, the extent of ionization suppression caused by co-extracted humic acids was examined in an ion trap mass spectrometer (MS), and a single quadrupole MS. It was found that under positive electrospray ionization, the single quadrupole MS was less susceptible to ionization suppression than the ion trap MS. Therefore, various sample clean-up procedures were evaluated to selectively reduce the amount of co-extracted humic acids in the soil extracts. The most effective clean-up was obtained from the use of Strata-X(TM) sorbent in combination with a strong anion exchange cartridge.