engleski

Electrophoretic behaviour and pka determination of human and veterinary antibiotics

Relevant processes regarding antibiotics in the environment include sorption to soils and sediments, complexation with metals and organics, chemical oxidation with natural or water treatment oxidants, photolysis, volatilization, biodegradation, purification, and analytical isolation. Because most antibiotics have acidic and/or basic functionalities, their ionization state is controlled by both solution pH and acidic dissociation constants of antibiotics (i.e., pKa values). Different chemical species (cationic, neutral, or anionic) often have vastly different properties with respect to water solubility, volatility, UV absorption, and reactivity with chemical oxidants. Unfortunately, the pKa values of many relevant antibiotics are either not known accurately or not available at all. Therefore, there is a significant need to determine the dissociation constants for environmentally relevant antibiotics to essentially facilitate occurrence, fate and effects. In this study, capillary electrophoresis (CE) was used to determine the pKa’ s of common human and veterinary antibiotics, namely, sulfonamides, macrolides, tetracyclines, fluoroquinolones, and other miscellaneous antibiotics. The method is based on measuring the electrophoretic mobility of the solute as a function of pH. Mobility and pH data are fitted to a suitable model using nonlinear regression. These equations have two advantages. They permit the determination of pKa of analytes with the advantages of CE and also permit the prediction of the effect of pH on the electrophoretic behaviour of substances and then the prediction of the pH optimum for the separation methods, using the minimum of experimental measurements. From dissociation constants, the major species of antibiotics present in the environment (usually in neutral pH range) can be estimated.

capillary electrophoresis; veterinary pharmaceuticals; pKa

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