Water hardness as a photochemical parameter: tetracycline photolysis as a function of calcium concentration, magnesium concentration, and pH.
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.
Werner
Jeffrey J
JJ
Water Resources Science Program, University of Minnesota, 1985 Buford Avenue, St. Paul, Minnesota 55108, USA.
Arnold
William A
WA
McNeill
Kristopher
K
D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002118:Calcium / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000032:analysis*; D010777:Photochemistry; D010782:Photolysis; D013056:Spectrophotometry, Ultraviolet; D013752:Tetracycline / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D000900:Anti-Bacterial Agents; D014867:Water; D013752:Tetracycline; D008274:Magnesium; D002118:Calcium