EFFECT OF SURFACE-ACTIVE AGENTS ON THE BINDING PROPERTIES OF MOLECULARLY IMPRINTED POLYMERS

Most analytical applications of MIPs showed the importance of minimizing non-specific interactions between the polymer and the sample matrix to improve their performance. Such non-specific interactions are generally based on weak hydrophobic forces between the polymer surface and the less hydrophylic components of the sample matrix. Consequently, additives able to interfere with such interactions should be able to reduce significantly any non-specific binding effect. Among the possible additives, surface-active agents represent an interesting classes of substances as they are cheap, easily available and compatible with the organic solvents commonly used.

Here we report a study of the effect of several surface-active agents on the binding properties of two different MIPs chosen to represent polymers based on ionic (2,4,5-trichlorophenoxyacetic acid, 2,4,5-T) or hydrogen bond (carbamazepine, CBZ) interactions in the binding site, respectively. HPLC columns packed with imprinted and non-imprinted polymers were eluted with mixtures of water/acetonitrile (containing acetic acid 1% v/v) added with variable amounts of three different surfactants: the anionic sodium dodecylsulphate (SDS, 0-0.2% w/v), the cationic cetyltrimethylammonium bromide (CTAB, 0-0.2% w/v) and the non-ionic polyoxyethylene-(20)-sorbitan monolaurate (Tween 20, 0-2.5% w/v).

The binding ability of the polymers towards the templates was evalued by measuring the capacity factors of these ligands and comparing the imprinting factor in the presence and absence of the surface-active agent.

The experimental results showed that in the case of 2,4,5-T-imprinted polymer surface-active agents are able to increase the imprinting effect by decreasing the non-specific binding. This effect is less marked with the non-ionic surfactant respect to the two ionic ones. This indicates that surfactants act mainly by inhibiting the ionic pair interaction between the acidic ligands and the basic functional monomer 4-vinylpyridine. On the contrary, in the case of CBZ-imprinted polymer no effect was observed for any surface-active agent used, indicating that such additives are not able to interfere with the hydrogen bond between the ligand and methacrylic acid. About selectivity, all the surfactants show no influence, as any increase of selectivity observed can be directly related only to the amount of water present in the mobile phase