Pharmaceutical compounds represent a rapidly emerging class of environmental contaminants. Such compounds were recently classified by the U.S. Geological Survey, including several antibiotics. An LC-MS/MS screening method for the top five antibiotics in drinking water was developed and validated using a Shimadzu LC-MS-IT-TOF. The separation was performed using a Waters Acquity UPLC BEH C18 column with a gradient elution. Sulfamethazine was exposed to conditions intended to mimic drinking water chlorination, and samples were collected and quenched with excess sodium sulfite. Kinetics of sulfamethazine degradation was followed as well as the formation of the major chlorinated byproduct ( 313). For the screening method, all five antibiotic peaks were baseline resolved within 5 minutes. Additionally, precision and accuracy of the screening method were less than 15%. Degradation of sulfamethazine upon exposure to drinking water chlorination occurred by first order kinetics with a half-life of 4？min (approximately 37 days) with measurements starting 5 minutes after chlorination. Likewise, the formation of the major chlorinated product occurred by first order kinetics with a rate constant of ？2. The proposed identification of the chlorinated product was 4-amino-(5-chloro-4,6-dimethyl-2-pyrimidinyl)-benzenesulfonamide (C12H13N4O2SCl) using spectra and databases searches of SciFinder and ChemSpider. 1. Introduction For over thirty years, pharmaceutical compounds have been emerging as environmental contaminants, appearing in drinking and waste water all over the world. The persistence of pharmaceutical environmental contaminants, such as antibiotics, in the water supply is of increasing concern within the field of environmental toxicology. Several domestic and international entities have reported the presence of antibiotic compounds in ground water, municipal drinking water, and waste water. Some of these antibiotics include sulfonamides, fluoroquinolones, chloramphenicol, and trimethoprim [1–6]. A recent survey of 47 groundwater sites across 18 states conducted by the U.S. Geological Survey found the common veterinary and human antibiotic, sulfamethoxazole, to be present in 23% of the samples collected [7]. Similar results associated with high environmental levels of sulfamethoxazole were found in a survey of the Seine River in France [2] and the Guangzhou section of the Major Pearl River, China [3]. While the absolute concentration of these drugs in drinking water is certainly subclinical, their presence has the potential to contribute to the emergence of
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