Research On Aqueous Determination And Photodegradation Of Oxytetracycline

Antibiotics are widely used in medical and animal husbandry,of which about 50%to 90%are not completely absorbed and excreted into environment in the form of parent compound or metabolites.Tetracyclines(TCs)are used as broad spectrum antibiotics,whose accumulation in the environment will break the balance of environmental microorganisms,accelerate the selection of resistance genes and treat human health through the enrichment of food chain.As a new type of pollutants,more and more attention is paid to TCs.Firstly,a method combining solid phase extraction(SPE)with high performance liquid chromatography(HPLC)was developed for the simultaneous determination of four TCs oxytetracycline(OTC),tetracycline(TC),chlortetracycline(CTC)and doxycycline(DC)in environmental water.The samples were cleaned up and pre-concentrated by the polar enhanced polymer(PEP)cartridges,separated by HPLC using 0.01 mol/L oxalic acid:acetonitrile:methanol = 7:2:1 as mobile phase and detected with wavelength 355 nm.The results showed a good linear correlation within 0.10 to 10.00 mg/L(R2>0.999).The method limits of detection ranged from 0.2 to 0.5 ?g/L,limits of quantification was 0.5?2 ?g/L.Recoveries were between 80.32%and 104.9%with relative standard deviations of 2.54%?7.85%.The method is convenient,rapid and reproducible which is suitable for analysis of TCs in environment.Research on the stability of TCs indicated that increasing temperature and illumination accelerated the decomposition of TCs while the influence of nature organic matter showed two sides.Photochemical degradation is the main pathway for the degradation of TCs in aquatic environments.In this study,OTC was chosen as a representative of TCs.The photolysis kinetics of OTC under the irradiation of UV-254 light source was systematically studied,the effects of operating conditions such as reaction time,initial concentration of OTC,dissolved oxygen,light source power,reaction temperature and initial pH,and the concentration of common anions in water environment such as NO3-?Cl-?SO42-and HCO3-,cation including Fe(?)?Ca2+ and Mg2+ and humic acid dissolved in water were investigated.The results showed that OTC photolysis followed pseudo first order model kinetics.The photolysis rate depended on initial OTC concentration,with k value ranging from 0.0496 min-1 to 0.0208 min-1,the OTC concentration increased from 2 mg/L to 40 mg/L.The higher concentration of dissolved oxygen inhibited the photolysis of OTC.The photolysis rate was facilitated as raising temperature and light source power.pH was a key factor controlling photolysis rate,OTC photolysis rate was significantly improved with increasing pH,with a half-life of 2.48 min at pH 11.5.Enhanced OTC photolysis rate was observed in the presence of NO3-and HCO3-.SO42-and low concentration Cl-had no significant effect on the degradation of OTC,but the high concentration Cl-could promote OTC photolysis.OTC photolysis was increased by Fe(?)due to its photosensitization and Ca2+ and Mg2+ because of their complexation with OTC.An acceleration of OTC photodegradation was observed at low HA concentration whereas suppression at HA concentration over 3 mg/L.To solve the problem that single UV could not completely mineralize OTC,it was studied that the removal efficiency of OTC by UV/H2O2 using the removal rate of total organic carbon(TOC)as an indicator.The reaction kinetics of OTC under different conditions was investigated,and the influences of reaction time,H2O2 initial concentration and pH on the reaction rate constant and TOC removal rate were explored.The results indicated that degradation of OTC by UV/H2O2 followed pseudo first order model kinetics under different conditions.When the dosage of H2O2 was 0.5?20 mmol/L,the reaction rate constant and TOC removal rate firstly increased and then decreased with the increase of H2O2 concentration.Neither strong acid nor strong alkaline condition was beneficial to the reaction.When H2O2 adding amount was 3 mmol/L,initial pH = 5.5,reaction rate constant was the largest,after 90 min reaction the highest TOC removal rate was up to 81.7%.