Department of Analytical Chemistry, University of Granada, Granada, Spain.
J Chromatogr A. 2011 Oct 14;1218(41):7289-96. doi: 10.1016/j.chroma.2011.08.043. Epub 2011 Aug 18.
In the current work, a molecularly imprinted polymer (MIP) has been synthesised and used to enable the extraction of a naturally-occurring antioxidant from complex media. More specifically, we describe the first example of a caffeic acid (CA) MIP which has been synthesised in the form of well-defined polymer microspheres, and its use for the extraction of CA from fruit juice sample. The CA MIP was synthesised by precipitation polymerisation using 4-vinylpyridine as functional monomer, divinylbenzene-80 as crosslinker and acetonitrile:toluene (75/25, v/v) as porogen. The particle sizing and morphological characterisation of the polymers was carried out by means of scanning electron microscopy (narrow particle size distribution; ∼5 and 1.5 μm particle diameters for the MIP and NIP [non-imprinted polymer], respectively) and nitrogen sorption porosimetry (specific surface areas of 340 and 350 m(2)g(-1), and specific pore volumes of 0.17 and 0.19 cm(3)g(-1) for the MIP and NIP, respectively). The polymers were evaluated further by batch rebinding experiments, and from the derived isotherms their binding capacity and binding strength were determined (number of binding sites (N(K))=0.6 and 0.3 mmol g(-1) for the MIP and NIP, respectively, and apparent average adsorption constant (K(N))=10.0 and 1.6L mmol(-1) for the MIP and NIP, respectively). To evaluate the molecular recognition character of the MIP it was packed into a stainless steel column (50 mm × 4.6 mm i.d.) and evaluated as an HPLC-stationary phase. The mobile phase composition, flow rate, and the elution profile were then optimised in order to improve the peak shape without negatively affecting the imprinting factor (IF). Very interesting, promising properties were revealed. The imprinting factor (IF) under the optimised conditions was 11.9. Finally, when the imprinted LC column was used for the selective recognition of CA over eight related compounds, very good selectivity was obtained. This outcome enabled the direct extraction of CA in commercial apple juice samples with recoveries in excess of 81% and, rather significantly, without any need for a clean-up step prior to the extraction.
在目前的工作中，合成了一种分子印迹聚合物（MIP），并将其用于从复杂介质中提取天然抗氧化剂。更具体地说，我们描述了第一个合成的咖啡酸（CA）MIP 的例子，它是以明确定义的聚合物微球的形式合成的，并将其用于从果汁样品中提取 CA。CA MIP 是通过沉淀聚合合成的，使用 4-乙烯基吡啶作为功能单体，二乙烯基苯-80 作为交联剂，乙腈：甲苯（75/25，v/v）作为致孔剂。聚合物的粒径和形态特征通过扫描电子显微镜（粒径分布较窄；MIP 和 NIP[非印迹聚合物]的粒径分别为 5 和 1.5 μm）和氮气吸附比表面积法进行（MIP 和 NIP 的比表面积分别为 340 和 350 m2g-1，比孔体积分别为 0.17 和 0.19 cm3g-1）。进一步通过批量再结合实验对聚合物进行了评价，并从所得的等温线确定了它们的结合容量和结合强度（MIP 和 NIP 的结合位点数（N（K））分别为 0.6 和 0.3 mmol g-1，表观平均吸附常数（K（N））分别为 10.0 和 1.6L mmol-1）。为了评估 MIP 的分子识别特性，将其填充到不锈钢柱（50mm×4.6mm i.d.）中，并作为 HPLC 固定相进行评价。然后优化了流动相组成、流速和洗脱曲线，以在不影响印迹因子（IF）的情况下改善峰形。非常有趣的是，显示出了有前景的性能。在优化条件下的印迹因子（IF）为 11.9。最后，当使用印迹 LC 柱对 CA 与八种相关化合物进行选择性识别时，获得了非常好的选择性。这种结果使得可以直接从商业苹果汁样品中提取 CA，回收率超过 81%，而且非常重要的是，在提取之前不需要进行净化步骤。
