三维荧光与紫外光谱联合表征样品中猝灭剂赋存状态:以胡敏酸与Fe(Ⅲ)相互作用为例

Characterizing the Existence of Fluorescence Quenching Agents Using EEM Fluorescence and UV Spectra:Taking the Interaction of Humic Acid and Fe(Ⅲ) as an Example

利用三维荧光-紫外光谱表征了荧光猝灭剂的赋存状态,当样品体系中存在Fe(Ⅲ)的情况下,胡敏酸会发生荧光猝灭现象,而其紫外光谱基本不受影响。考察了胡敏酸荧光强度I值(Ex/Em=300 nm/510nm)和紫外吸光度A值(UV300)的变化,I/A比值越小,说明水样中猝灭剂Fe(Ⅲ)浓度越高。当胡敏酸为10,15和20 mg·L^(-1)时,根据Stern-Volmer公式I/I_0=1-f_c×K_c×[c]/(1+K_c×[c])以及拟合函数I/A=f×[k/(CFe^(3+)+c)+b],拟合得到荧光猝灭常数K_c=1.08~1.15,比例系数f_c=1.10~1.14之间,胡敏酸荧光强度值与吸光度比值(I/A)及铁离子浓度(C_(Fe^(3+))相关曲线系数f=0.83~1.19,k=587.19~612.19,c=0.87~0.92,b=-87.09^-46.36,拟合曲线相关性R^2均为0.99。Stern-Volmer公式描述了Fe(Ⅲ)对胡敏酸荧光的猝灭作用,但实际样品测定时难以获得无猝灭剂时的荧光强度I_0。基于荧光强度I_0与紫外吸光度A之间的内在联系,两者比值I/A与Fe(Ⅲ)浓度c的拟合函数亦可以反映Fe(Ⅲ)对胡敏酸荧光的影响。利用拟合公式预测城市污水厂及纳污河流样品的树脂分离富集液中铁离子浓度,与电感耦合等离子体发射光谱仪实际测量值相比,铁离子浓度较高的情况下(铁离子浓度大于0.4 mg·L^(-1)时)预测结果较好,可以判断猝灭剂的存在及相应浓度。

The fluorescence quenching agents was characterized with three-dimensional fluorescence and ultraviolet（UV） spectra.When there was Fe（Ⅲ） in the sample,the humic fluorescence would be quenched and their UV spectra were not affected.The variation of fluorescence intensity（I） at Ex/Em= 300/510 nm and UV absorbance（A） at UV300 were investigated in the article.The smaller the ratio of fluorescence intensity versus UV absorbance（7/A） is,the higher the fluorescence quencher Fe（Ⅲ） concentration is.According to Stern-Volmer equation I/I_0 = 1-f_c×K_C×[c]/（l ＋ K_c×[c]） and fitted function I/A= f×[k/（c_（Fe^（3＋）） ＋c）＋b],the fitted fluorescent quenching constant K_c was ranged between 1.08 to 1.15,the ratio of bounded fluorophores versus total fluorophores,i.e.f_c,was ranged between 1.10 to 1.14.The ratio of fluorescence intensity and absorbance of humic acid was fitted with Fe（Ⅲ） concentration and the constants were acquired as following：f= 0.83~1.19,k =587.19 ~ 612.19,c=0.87~0.92,b=-87.09^-46.36.The correlation curve values were 0.99.The Stern-Volmer formula was used to describe the quenching effect of humic acid fluorescence by Fe（Ⅲ）.However,due to the fact that the fluorescence intensity 10 without quencher was difficult to acquire during the analysis of practical samples,the fitted function between the ratio of I/A and Fe（Ⅲ） was used to reflect the quenching effect of Fe（Ⅲ） on the fluorescence of humic acid,which was based on the correlations between the fluorescence intensity I_0 and ultraviolet absorbance A.The fitted formula was used to predict the iron ions concentration of the resin separated and concentrated samples from wastewater treatment plant and receiving waters.The predicted values were in good accordance with those determined with inductively coupled plasma atomic emission spectroscopy（ICP-AES） method when the iron ion concentration was above 0.4 mg ？ L^（-1）,which could be used to ascertain the existence of fluorescence quenching agent and their corresponding concentration.