新型强阳离子交换聚合物整体柱的制备及其在奶制品中三聚氰胺测定中的应用

在内径为530 μm的石英毛细管中原位聚合得到一种新的强阳离子交换聚合物整体柱2-丙烯酰胺-2-甲基-1-丙磺酸-乙二醇二甲基丙烯酸酯聚合物(poly(AMPS-co-EDMA))整体柱,并将其作为聚合物整体柱微萃取(PMME)的萃取介质。优化N,N-二甲基甲酰胺(DMF)和聚乙二醇(PEG)致孔体系的比例,制备得到的poly(AMPS-co-EDMA)整体柱渗透性好、机械强度高且在水溶液中具有良好的稳定性。通过考察样品溶液的pH值、盐浓度和有机溶剂含量对萃取效率的影响,证明该整体柱主要通过强阳离子交换和疏水相互作用对三聚氰胺进行萃取富集。在PMME与高效液相色谱联用技术的基础上,建立了检测奶制品中三聚氰胺含量的分析方法。奶制品中三聚氰胺的检出限和定量限分别为0.09 mg/kg和0.3 mg/kg,在0.5~80 mg/kg的含量范围内具有良好的线性关系,日内、日间测定的相对标准偏差不高于7.5%。结果表明,该方法简便、快速、灵敏度高且成本低,适合于奶制品中微量三聚氰胺的检测。

Preparation of a strong cation-exchange polymer monolith and its application in determination of melamine in milk products

A poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-ethylene dimethacrylate) (AMPS-co-EDMA) monolith was prepared in a fused-silica capillary (530 μm i.d.) and applied for polymer monolith microextraction (PMME). With the optimal ratio of N,N-dimethylformamide (DMF, porogen) and polyethylene glycol (PEG, co-porogen), the resulting monolith exhibited satisfactory permeability, high mechanical strength and good stability in aqueous buffer. The effects of several parameters to PMME were investigated, such as pH value, inorganic salt and organic phase concentration of the sample matrix. It demonstrated that the melamine was captured on the poly(AMPS-co-EDMA) monolith mainly through strong cation-exchange and hydrophobic interactions. A novel approach is presented for the determination of melamine in milk products by coupling PMME to high performance liquid chromatography with ultraviolet detection. Because of the high extraction capacity of the monolith towards melamine, low detection limits (S/N=3, 0.09 mg/kg) and quantification limits (S/N=10, 0.3 mg/kg) were obtained. The method showed good linearity ranging from 0.5 to 80 mg/kg. Excellent reproducibility of the method was exhibited by intraday and interday precisions, yielding the relative standard deviations not larger than 7.5%. The proposed method is simple, rapid, sensitive, and low cost.