Preparation Of Molecularly Imprinted Polymers Using Melamine As The Template And Its Application In Milk Powder

In recent years, the issues of food safety have emerging more and more, which attract attention of the people around the world. The food safety has become a focus of all the people. So it is very important to develop an effective detection method to meet the need of the food safety. As the molecular imprinted polymers (MIPs) has the intended function, deliberately choice, stability of physical and chemical, wide using. The technology of food safety determination based on molecular imprinted polymer has become a new trends. In this paper, a high adsorption capacity molecularly imprinted polymers have been prepared for selectively recognizing melamine. The conditions of polymerization, including functional monomer, cross-linnker and so on, were optimized and the MIPs with the best specific adsorption capacity to melamine was obtained. At last the MIPs were applied as the sorbent of solid phase extraction (SPE) and the procedure of molecularly imprinted polymer solid phase extraction (MISPE) was optimized, and then applied in the detection of trace melamine in milk powder. Subsequently, the electrochemical measurements of melamine were carried out using potassium ferricyanide as a electrochemical probe and MIPs as recognition element. The detection conditions, such as pH value of supporting solution, amount of MIPs, accumulation potential and time were investigated. The main contents of this research are described as follows:1. A series of melamine molecularly imprinted polymers were prepared by precipitation polymerization. The compositions of polymers, including the porogenic solvent, the functional monomer and the cross-linker were optimized. The MIPs with the best affinity to the template was obtained. The compositions of the best-performing MIPs were as follows: 0.3 mmol melamine, 4.2 mmol functional monomer (Methacrylic acid, MAA), 20 mmol crosslinker (Ethyleneglycol dimethacrylate, EGDMA), 40 mg initiator (Azodiisobutyronitrile, AIBN) were dissolved in 60 mL of methanol/acetonitrile (18/82, V/V), and the mixture was polymerized at 60℃for 24 h. Chromatographic evaluation showed that the imprinting factor of the best-performing MIPs was 7.53, and the total amount of the immobilized ligand was 44.8μmol/g. The polymer particles were regular examined by Scanning electron micrograph. At last, the hydrogen bond between MIPs and the template was confirmed by infrared spectrum.2. The best-performing MIPs was applied as the sorbent of SPE. The conditions of MISPE, including loading, washing and eluting, were optimized. The optimal MISPE protocol was loading with methanol, washing with 2 mL acetonitrile and eluting with 3 mL 5% ammonia/methanol (V/V) solution. Under this protocol, the recovery of the melamine through MIPs column was from 85.1% to 99.7%, and the recovery of non-imprinted polymer solid phase extraction (NISPE) column was only 19.4%. Compared with National standard method (GB/T 22388-2008), obtained a better purification results and high recoveries, which can meet the needs of the actual testing work.3. A selective, sensitive, rapid and reliable method based on melamine-MIPs modified glassy carbon (GC) electrode was prepared to detect trace melamine with potassium ferricyanide as an electrochemical probe. Compared with bare and NIPs modified GC electrode, the MIPs modified GC electrode exhibited excellent sensitivity in the low concentration of melamine and lower detect limits. Under the optimized conditions, the linear range is from 1.6 nmol/L to 47.6 nmol/L. The limit of detection was significantly reduced to 1.6 nmol/L.