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() Identification of a photooxygenation product of chlortetracycline in hog lagoons using ion-trap and time-of-flight mass spectrometry.
Eichhorn, P.1, Aga, D.1, 1 State University of New York at Buffalo, Buffalo, NY, USA
ABSTRACT- Modern animal husbandry practices encountered in large-scale confined animal feeding operations (CAFOs) rely on the extensive use of antibiotics for prevention and treatment of diseases as well as for growth promoting purposes and to increase feed efficiency. Of the total amount of 9,900 metric tons of antibiotic compounds sold to U.S. farmers in the year 2001, about one third belonged to the class of tetracycline antibiotics. These compounds are only partially metabolized and are mainly excreted via urine and feces in its original form. Therefore, the manure of treated animals contains appreciable levels of tetracyclines. In the present work, a photoproduct of chlortetracycline was identified for the first time in hog lagoon samples from CAFOs. A combined approach using the multiple-stage capabilities of ion trap-mass spectrometry (IT-MS) for structural elucidation and the ability of time-of-flightmass spectrometry (ToF-MS) in obtaining accurate mass measurements to allow the assignment of highly probable empirical formula led to the identification of a photooxygenation product of chlortetracycline (designated as M510). Generation of the assumed photoproduct was achieved in a 24 h-irradiation experiment of an oxygenated alkaline medium containing 50 mg L-1 chlortetracycline. Multiple-stage experiments in the IT-MS were performed in both positive and negative ion mode to produce second and third generation mass spectra. Similar characteristic fragmentation patterns in the mass spectra of isochlortetracycline were observed in the mass spectra of M510, suggesting that its structure consisted of an isochlortetracycline-like skeleton bearing two additional hydroxy groups. Accurate mass measurement of the postulated photooxygenation product (C22H23N2O10Cl) gave m/z 511.1109 for the protonated molecular ion corresponding to an error of +1.0 ppm. Quantitative analysis of seven hog lagoon samples showed isochlortetracycline concentrations of 1,910 to 15,800 
g L-1, while the levels of M510 were found to be between 46 and 303 g L-1. Further examination of chromatograms corresponding to hog lagoon samples indicated the occurrence of several isobaric compounds closely eluting to M510, hypothesized to be hydroxy isomers.
Key words: chlortetracycline, photodegradation, mass spectrometry, structure elucidation