Preparation Of Al₂O₃Modified Polymer Monolith And Its Application In The Separation And Determination Of Synthetic Dyes

As a novel separation and enrichment material, polymer monolith has shown severalattractive features including easy preparation, frit-free construction, good biocompatibility, andwide application range of pH. However, the swelling or shrinkage of polymer monoliths in somesolvents may result in the deficiency in mechanical stability.Recently, functionalization of monoliths with nanoparticles has been rapidly developedwhich features a very high surface-to-volume ratio and distinctive chemical property. γ-Al2O3nanoparticles are porous inorganic material with adjustable pore dimensions (10-20nm), whichhave the advantages of the uniformity of particle size, large surface area, high porosity, strongability of adsorption, and excellent dispersibility in many organic solvents. In this paper, γ-Al2O3nanoparticles modified monolithic columns were prepared and used for polymer monolithmicroextraction (PMME) coupled to HPLC for the determination of synthetic dyes in food. Itincludes the following two sections.1. Poly(N-isopropylacrylamide-co-N, N’-methylene bisacrylamide) monolithic columnembedded with γ-Al2O3nanoparticles has been prepared. The novel monolithic column was usedas the separation and enrichment medium by coupling with HPLC-DAD for the determination ofsynthetic dyes (Tartrazine, Sunset Yellow, Allura Red, Azorubine) in soft drinks. In thisexperiment, the HPLC conditions were optimized as follows. The mobile phase consisted of Aand B (A:B=55:45, V/V), where A represented0.1mol/L aqueous ammonium acetate solution,B represented a mixture of methanol:acetonitrile (80:20, V/V). The flow rate of eluent wasalways kept constant at0.8mL/min and the injection volume was set at5μL. The columntemperature was set at35oC. The determination of each target was employed at the appropriateabsorbance wavelengths, i.e.,427nm for Tartrazine,490nm for Sunset Yellow,507nm forAllura Red, and520nm for Azorubine. The PMME conditions which would influence the extraction efficiency were investigated. The optimum PMME conditions were: sample pH of4.0,sample flow rate of0.03mL/min, sample volume of0.8mL, and eluent flow rate of0.05mL/min. Under the optimal experimental conditions, the LODs of analytes varied in the range of9.311.5ng/mL. The intra-day and inter-day RSDs were in the range of3.76.1%and5.69.8%,respectively. Satisfactory recoveries were obtained in the range of90.4109.2%, exhibiting thatthe present method is effective for the determination of Tartrazine, Sunset Yellow, Allura Red,and Azorubine in soft drinks.2. We designed and synthesized a new type of γ-Al2O3nanoparticles coated-poly(N-isopropylacrylamide-co-glycidyl methacrylate-co-ethylene dimethacrylate) monolithiccolumn via a chemical bonding method. In order to access satisfactory extraction efficiency andmechanical stability of the modified monolithic columns, we optimized the conditions of themodification procedure, the concentration of NaOH solution, and γ-Al2O3nanoparticlesdispersion. This monolithic column was used as the separation and enrichment medium bycoupling with HPLC for the determination of Sudan dyes in red wine samples. In order to gethigh extraction efficiency, various parameters influencing the extraction efficiency have beenoptimized, such as sample pH, sample flow rate, sample volume, desorption solvent type, andeluent flow rate. Under the optimum conditions, the method provided a relatively low limits ofdetection (0.130.29ng/mL). The intra-day and inter-day precisions of the present method werein the range of3.14.7%and4.15.7%, respectively. The recoveries of Sudan I-IV dyes wereobtained in the range of84.0115.9%with RSD values less than7.1%, which exhibited that thepresent method is effective for the determination of Sudan I-IV dyes in red wine samples.