Water hardness as a photochemical parameter: tetracycline photolysis as a function of calcium concentration, magnesium concentration, and pH |
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Authors: | Werner Jeffrey J Arnold William A McNeill Kristopher |
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Affiliation: | Water Resources Science Program, University of Minnesota, 1985 Buford Avenue, St. Paul, Minnesota 55108, USA. |
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Abstract: | The environmental photochemical kinetics of the antibiotic compound tetracycline were investigated. The aqueous speciation of tetracycline over a range of natural pH and water hardness values is dominated by association with Ca2+ and Mg2+ ions. The association constants necessary to calculate tetracycline aqueous speciation given knowledge of pH, [Ca2+], and [Mg2+] were measured by spectrophotometric titrations and matrix deconvolution of a series of UV-vis absorption spectra into individual component species. A series of photolysis experiments was performed under simulated sunlight, and quantum yields for the solar photolysis of each environmentally relevant species were calculated. The results indicate that the pseudo-first-order rate constant for tetracycline photolysis at varied Mg2+ and Ca2+ concentrations relevant to natural conditions can vary by up to an order of magnitude. A self-sensitization effect was observed and was accounted for by varying the initial tetracycline concentration under each set of photolysis conditions. |
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