Characterization of DOM complexation with heavy metals based on characteristic fluorescence spectroscopy
The fluorescence quenching method can be used to characterize the reaction of DOM with pollutants.When excitation(e-mission)and synchronous fluorescence spectra are applied,the selection of Em(Ex)and Δ λ(λem-λex)will affect the expression of spectral information.The complexation between DOM and heavy metals in surface water of Chaohu Lake was studied by fluorescence quenching method with DOM,L-tryptophan and sodium humate solution as the research object,Cd2+as the target heavy metal.The results show that the three-dimensional fluorescence spectra of the three groups of quenching systems can be divided into four re-gions:low excited state tryptophan(S),high excited state tryptophan(T),humic acid-like(C)and fulvic acid-like(A).The fluores-cence intensity was relatively quantified by the integrated volume of the fluorescence region.Under the initial state,the integrated volume of the fluorescence region of the DOM in the surface water of Chaohu Lake was A＞C＞T＞S,which was humic-like dominant.With the increase of Cd2+concentration(0-7 mg·L-1),the integrated volume of the fluorescence regions in the four regions of the three quenching systems decreased.The quenching efficiency of Cd2+on the fluorescence region of DOM in the surface water of Cha-ohu Lake was S＞T＞A＞C,the quenching efficiency of L-tryptophan was S＞T,and the quenching efficiency of sodium humate was C＞A.The synchronous fluorescence spectra(Δλ=60 nm)of the three quenching systems decreased with the increase of Cd2+concen-tration(0-7 mg·L-1).From the three-dimensional fluorescence spectrum,it can be seen that the synchronous fluorescence spec-trum of Δλ=60 nm(Ex=200-450 nm)only passed through the T and C regions,and did not pass through the S and A regions.Some characteristic fluorescence bands of the three quenching systems were lost.According to the characteristics of the three-dimen-sional fluorescence spectrum,the excitation spectrum(Em=350 nm,450 nm)was selected to obtain three sets of excitation spectrum curves of the quenching system,and the intensity change trend of the characteristic spectral bands in the four fluorescence regions was expressed.In this study,the linear spectrum was selected according to the three-dimensional fluorescence spectrum of the quenching system,which can selectively characterize the change of the characteristic fluorescence information of the quenching sys-tem,and provide an effective analysis technique for studying the interaction between DOM and pollutants.
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