Preparation Of Two Novel Types Of Rhodamine B Molecularly Imprinted Polymers And Application In Food Analysis

Rhodamine B is a type of synthetic dye.It is widely used for cell fluorescence staining,paper printing,and textile dyeing industries.However,it has been introduced to foodstuffs gradually due to their colorfastness and low cost.In China,Rhodamine B has been existed in the list of illegal food additives and forbidden in foodstuffs because it is harmful to human beings and animal.Unfortunately,the contamination of Rhodamine B in food is still occurred under some circumstances.Analytical techniques have been used for determination of Rhodamine B,like HPLC and HPLC-MS.However,because the matrix of sample is very complex in the processs of determination,it is necessary to build a high perfomance sample-preparation method that can isolate and concentrate target analytes.In this study,two novel molecularly imprinted polymers grafted onto the surface of carboxyl-modified multi-walled carbon nanotubes and magnetic Fe3O4 nanoparticles,which possess the specific ability to bind to Rhodamine B,were developed using methacrylic acid as a functional monomer and trihydroxymethylpropyl trimethylacrylate as a crosslinker.A pretreatment method which using the molecularly imprinted polymers as adsorbent was developed for the determination of Rhodamine B in the real samples with types of powder,sauce and liquid using spectrophotography.The main results are as follows:Molecularly imprinted polymer grafted onto the surface of carboxyl-modified multi-walled carbon nanotubes,which possess the specific ability of binding Rhodamine B.was developed.Optimization for preparation molecularly imprinted polymer was achieved using the orthogonal analysis after single-factors test.The results were as follows:the ratio of template moleculer:function monomer:cross-linker was 1:4:20,temperature was 60 ?,porogen was 50 mL.The imprinted polymer was characterized,and exhibited good recognition ability and fast adsorption-desorption dynamic toward the Rhodamine B.Equilibrium binding experiments were conducted and revealed the maximal binding capacity to be 561.54 ?g/g.The introductions of nanomaterial into the polymer-composite make important contributions to the affinity enhancement and recognition properties of the molecularly imprinted polymer.Moreover,the polymer was preliminarily applied as an adsorbent for separation and extraction of Rhodamine B from real samples,based on solid phase extraction technology coupled with spectrophotometer.Various parameters which probably influence efficiency of extraction were optimized.The optimum parameters were as follows:extraction solvent was acetonitrile,washing solvent was n-hexane,eluent was methanol,amount of MIP was 0.5 g and flow rate was 1 mL/min.And the proposed method was applied to analysis of Rhodamine B under the optimal experimental conditions.The recoveries for analytes were in the range of 97.60%-99.01%and relative standard deviation values for six replicate were found to be lower than 5%.The limits of detection and quantification were 2.57 ?g/g and 8.56 ?g/g,respectively.This demonstrated that the polymer has potential for preconcentration of Rhodamine B from real samples.A novel magnetic material based on the use of Fe3O4 nanoparticles coated with molecularly imprinted polymer was developed using Rhodamine B as a template.The prepared magnetic molecularly imprinted polymer possessed the specific ability of binding Rhodamine B after treatment with eluent.The polymer was characterized by scanning electron microscopy,Fourier-transform infrared spectroscopy,and thermo-gravimetric analysis.Static adsorption,kinetic adsorption,and selective recognition experiments were also performed to investigate the specific adsorption equilibrium,kinetics,and selective recognition ability of the polymer.The magnetic molecularly imprinted polymer had outstanding thermal stability,large adsorption capacity,and high competitive selectivity.Moreover,we developed a method to detect Rhodamine B by using the polymer as dispersed solid-phase extraction adsorbents coupled with spectrophotometer.Various parameters which probably influence efficiency of extraction were optimized.The optimum parameters were as follows:extraction solvent was water,adsorption time was 20 min,amount of MIP was 25 mg,eluent was methanol,and desorption time was 10 min.And the proposed method was applied to analysis of Rhodamine B under the optimal experimental conditions.The recoveries for analytes were in the range of 74.16%?81.88%and relative standard deviation values for six replicate were found to be lower than 5%.The limits of detection and quantification were 1.05 pg/L and 3.49 ?g/L,respectively.In addition,the polymer can be separate from the solution by magnetic field because of the magnetism from Fe3O4 nanoparticles.This will be help to omit the repeated centrifugation procedure and improve the accuracy of the results.The polymer could be used for several times with only slight loss in specific adsorption behavior.