Effect Of Dissolved Organic Matter And Mechanism On The Adsorption And Desorption Of Ofloxacin Enantiomers On Goethite

As we know,there are many studies about antibiotics,which as an emerging contaminant in the environment.However,there are relatively few studies on chiral antibiotics or other chiral substances,especially about the adsorption of chiral antibiotics on minerals or other media.This paper studied the optimal method for separate and determined OFL and levofloxacin?LEV?simultaneously;the interaction between OFL and LEV on goethite;the influence of DOM on the fractionation?adsorption and desorption?of OFL and LEV on goethite was studied using batch and column experiments.The results showed that:?1?High performance liquid chromatography?HPLC?method can simultaneously determine OFL chiral isomers.The analysis conditions were:mobile phase volume ratio of methanol/water?including 4 mmol/L isoleucine and 3 mmol/L CuSO₄?were20/80,the water phase of the mobile phase pH were 4.5,column temperature of 40?,the flow rate were 1 mL/min,detection wavelength were at 293 nm and 20 mL injection volume.The two antibiotics were separated within 18 min with a resolution of 2.7.In addition,the influences of metal cation(Ca²⁺,Mg²⁺,Zn²+,Fe³⁺)and humic acid on the test were studied.The results showed that both metal cation and humic acid had negative effects on the test,Fe³⁺had the most significant influence,and the concentration of the OFL chiral isomer decreased with the increasing concentration of humic acid increased.?2?The adsorption capacity of OFL and LEV adsorbed on goethite changed as a function of pH.The largest adsorption amount of OFL and LEV was at the pH 5-6,and there was no significant difference between the two antibiotics.When the two antibiotics were coadsorbed on goethite,there was no interaction or prefer adsorption,but the infrared spectroscopy?IS?data showed that the complexation types of the two antibiotics with goethite were different.The complexation structure of OFL was double-bridge complexation,and the complexation types of OFL were bidentate chelation and double-bridge complex.?3?The effect of six kinds of DOM on OFL and LEV absorbed on goethite played a promote role,but the promoting effect for two antibiotics were in a different order.And the FTIR data of the interaction among DOM,antibiotics and goethite were investigated,it indicated that it was from OFL-DOM-goethite and LEV-DOM-goethite.The complexation of OFL-DOM-goethite was more complex,since phenol functional groups involved in the reactions.When the two antibiotics coadsorbed on goethite,DOM has different promoting effects on OFL and LEV,the higher the aromaticity,lower carboxylic acid content and higher phenol content cause the higher enantioselectivity for OFL.?4?The results of the column experiment showed that the column which preload DOM reached the equilibrium later than the non-DOM column during the adsorption process,and OFL reached its equilibrium later than LEV.In the desorption process,the preload DOM column is more difficult to be desorbed completely than the non-DOM column,but OFL is more difficult to be desorbed completely than LEV.