Complexation Behavior Of Typical Pharmaceutical Antibiotics And Heavy Metals In Water

The combined pollution of antibiotics and heavy metals becomes more serious in the aquatic environment, resulting in increased stability and toxicity as well as the water safety risk. Therefore, it is necessary to study the complexation behavior of antibiotics and heavy metals to understand the interaction of antibiotics with heavy metals, which may provide a theoretical support to solve the threat of antibiotics and heavy metals combined pollution.Potentiometric titration was used to study the complexation behavior of three typical antibiotics (tetracycline, ciprofloxacin and sulfamethoxazole) and three typical heavy metal ions (Cu2+, Pb2+ and Cd2+) in water.The acid dissociation constant (pKa) of three typical antibiotics were obtained. The acid dissociation constants of TC were pKa1=3.38, pKa2=7.54, pKa3=9.36 seperately; the acid dissociation constants of CIP were pKa1=6.21 and pKa2=8.57; the acid dissociation constants of SMZ were pKa1=1.63 and pKa2=6.01. The speciations of TC were H3TC+, H2TC0, HTC- and TC2-; the speciations of CIP were CDP+, CIP0 and CIP-; the speciations of SMZ were SMZ+, SMZ0 and SMZ-.Through the experiment of potentiometric titration, the complexes and complexation constants (logK) of typical antibiotic and heavy metal ions were obtained. The speciations of TC-Me were MeHTC+ and MeTC0; the speciations of CIP-Me were MeCIP2+, MeCIP22+ and MeCIP2+; the speciations of SMZ-Me was MeSMZ+.For the three antibiotics, the complexing ability of heavy metal ions were in the order of Cu2+> Pb2+> Cd2+ at the ratio of antibiotics and heavy metal of 1:1. For the heavy metal ions, when the ratio of antibiotics and heavy metal was 1:1, the complexing ability of antibiotics were in the order of CIP>TC>SMZ at 3.0<pH<7.0; the complexing ability of antibiotics were in the order of TC CIP at 7.0<pH<9.0.Finally, XANES and ATR-FTIR were used to characterize the complexes of copper and antibiotics. The results showed that, the complex position of TC-Cu were the O on C3-position, the 0 on C11-position and the O on C2-position of TC; the complex position of CIP-Cu were the carboxyl (-COOH) on position three and the carbonyl (C=O) on position four of CIP the complex position of SMZ-Cu were sulfa oxygen (S=O) and the N on position one.