Journal of Chromatography A, 1314 (2013) 115–123 Contents lists available at ScienceDirect Journal of Chromatography A jou rn al hom epage: www.elsevier.com/locate/chroma Imidazolium-based functional monomers for the imprinting of the anti-inflammatory drug naproxen: Comparison of acrylic and sol–gel approaches Porkodi Kadhirvel a,∗ , Manuel Azenha a,∗ , Sudhirkumar Shinde b , Eric Schillinger b , Paula Gomes a , Börje Sellergren b , A. Fernando Silva a a CIQ-UP, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Portugal b INFU, Faculty of Chemistry, Technical University of Dortmund, Otto-Hahn-Str. 6, D-44221 Dortmund, Germany a r t i c l e i n f o Article history: Received 4 July 2013 Received in revised form 3 September 2013 Accepted 4 September 2013 Available online 9 September 2013 Keywords: Molecular imprinting Cationic monomer Sol–gel Methacrylic polymer Naproxen Frontal analysis a b s t r a c t Imidazolium-based monomers were, for the first time, employed in a comprehensive investigation of the molecular imprinting process of naproxen in both acrylic and sol–gel tridimensional networks. To this end, molecularly imprinted polymer (MIP) and xerogel (MIX) were both optimized for performance, by testing different porogen, template speciation and component ratios. The developed imprints were characterized for their pore properties (nitrogen adsorption analysis), site heterogeneity, binding prop- erties and other performance parameters such as the imprinting factor, selectivity (HPLC column tests), column efficiency and mass transfer kinetics (frontal analysis study). MIP exhibited mesoporosity (D p 29 nm), whereas MIX did not, which was reflected in both the lower number of accessible imprinted sites (4.9 mol/g versus 3.7 mol/g) and the slower binding/dissociation in MIX. The naproxen/ibuprofen selectivity ratio was estimated as 6.2 for the MIX and 2.5 for the MIP. Given the high importance of capac- ity and fast mass transfer in typical applications of imprinted materials, and the satisfactory selectivity of MIP, it can be concluded that the acrylic approach was globally the most advantageous. Still, the remark- ably high selectivity of MIX and its reasonable capacity demonstrate that future work devoted to further optimization of both formats is worthwhile. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Molecular imprinting is a versatile technique for preparing syn- thetic materials with tailored molecular recognition properties; as such, is presently attracting widespread interest, especially in chromatography, (bio)chemical sensing, drug delivery and cataly- sis [1]. The preparation of molecularly imprinted polymers (MIP) typically involves three steps: first, a monomer-template [M–T] complex is formed via self-assembly; next, the M–T complex is polymerized with an excess of cross-linker to form a rigid polymer; finally, the template is removed, leaving behind binding cavities which are complementary in shape and functional group to the template [2]. The vast majority of MIP is based on the use of organic acrylate-type polymers: a standard procedure using a methacrylate monomer, with a nearly optimal ratio to the template molecule and crosslinker, is described in numerous works [2–8]. The broad applicability of methacrylic acid (MAA) as a functional monomer ∗ Corresponding authors. Tel.: +351 220402628; fax: +351 220402659. E-mail addresses: porkodikathirvel@yahoo.com (P. Kadhirvel), mazenha@fc.up.pt (M. Azenha). in MIP production is related to the fact that the carboxylic acid group serves well as a hydrogen bond and proton donor as well as a hydrogen bond acceptor [9]. Nevertheless, a common severe con- straint of this type of imprinting is the need for an organic solvent in which all species are soluble. This further precludes use of template molecules that are only soluble in aqueous media, which implies obvious limitations in the development of MIP for many environ- mental and biological applications. Although some promise has been shown for aqueous-based rebinding procedures, such results are rare and considerable progress is required to overcome this limitation [10,11]. Sol–gel imprinting is one possible alternative for achieving molecular recognition of hydrophilic targets, given the ease of preparation of sol–gels and their compatibility with polar environ- ments [12]. Sol–gel imprinting is straightforward and provides an efficient way for preparing hybrid matrices through incorporation of organic components into inorganic polymers under mild thermal conditions, while controlling MIP thickness, porosity and surface area. However, to date, amorphous sol–gel molecularly imprinted xerogels (MIX) have not demonstrated the same degree of suc- cess as MIP for analytical applications, namely in the form of bulk materials. 0021-9673/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.chroma.2013.09.015