| Molecularly imprinted polymers (MIPs) are made by synthesizing highly crosslinked polymers in the presence of"imprint"molecules (the template). After removal of the template, the polymer can be used as a selective binding medium for the print molecule or other structurally analogues. In general, one kind of molecule is imprinted in MIPs to obtain high selectivity only to the template compound itself. Nevertheless, cross-selectivity is also useful for particular applications. Owing to cross-selectivity, MIPs, using dummy template with similar molecular structure to the target molecules, still have molecular recognition ability for target molecule. Additionally, another strategy is to obtain group selectivity by multi-templates imprinted polymer. In the present work, it was attempted to gain similar responses for all four kinds of parabens on the MIPs sensor based on multi-templates imprinted polymer. Accordingly, it is possible to determine the total contents of paraben rapidly in actual samples with the dual-templates MIPs sensor. On the other hand, multi-templates imprinted polymer has potential to detect analytes with nonanalogous structures simultaneously, as these target molecules imprinted in the polymer membrane. The main contents are listed as follows:In the first part, a selective, sensitive, rapid and reliable method based on molecularly imprinted polymers (MIPs) with dual templates to determine total content of parabens in cosmetics was developed. With methylparaben (MP) and propylparaben (PP) as dual-templates, methacrylic acid (MAA) as a functional monomer and tripropylene glycol diacrylate (TPGDA) as a cross-linker, MIPs film on a glassy carbon electrode was constructed as parabens sensor. Electrochemical oxidation behaviors of four kinds of parabens on the bare electrode and MIPs sensor had been investigated with square wave voltammetry. At oxidation potential of 0.94 V (vs.SCE), the peak currents on the MIPs sensor were proportional to the concentration of parabens. As the ratio of MP to PP in the MIPs was 1:1.25, the regression equations for four parabens were almost the same. The total content of parabens could be calculated according to the average of these four regress equations. The MIPs sensor displayed specific binding of parabens. At least 10 times of structural analogs, such as p-hydroxybenzoic acid, p-aminobenzoic acid and phenol would not interfere with the determination of parabens. Nonanalogous coexistences such as vitamin C had no response on the sensor at all. The RSD of peak currents of MP was 3.9% (n=5). MIPs sensor had been used to determine total content of parabens in cosmetic samples with recoveries between 98.7% and 101.8%. It reveals that the MIPs sensor with multi-templates has a potential to determine the total content of a group of homologous compounds.In the second part, a molecularly imprinted polymers(MIPs) film was synthesized on the surface of a glassy carbon electrode with the salicylic acid (SA) as template. Electrochemical oxidation behaviors of SA on the imprinted electrode was investigated by square wave voltammetry. As the incubation time of 6 min, the peak currents were proportional to the concentration of SA in the range from 1.0×10-5 to 2.6×10-4 mol/L with a detection limit of 2.0×10-6 mol/L (S/N=3). The RSD of peak currents was 3.7 % (n = 7). The imprined electrode displayed good specificity. The selective coefficients of structural analogs were 12 and 6.9 for p-hydroxybenzoic acid and p-aminobenzoic acid, respectively. The MIPs sensors had been used to determine SA in cosmetic samples with recoveries between 99.9 % and 106.7 %.In the third part, based on the above work, a multi-templates imprinted polymer film was synthesized on the surface of a glassy carbon electrode with the SA and PP as dual-templates, adjusting the ratio between the template molecules in order to develop multi-templates MIPs sensor which can investigate the content of SA and PP together. As the ratio of SA to PP in the MIPs was 3:1, the peak shape and resolution were the best. As the incubation time of 7 min, the peak currents were proportional to the concentration of SA in the range from 1.0×10-5 to 3.6×10-4 mol/L with a detection limit of 5.0×10-6 mol/L (S/N=3). And the peak currents were proportional to the concentration of PP in the range from 1.0×10-5 to 1.2×10-4 mol/L with a detection limit of 1.0×10-5 mol/L.The RSD of peak currents were 2.4 % and 2.6 % respectively (n = 5). The MIPs sensors had been used to determine SA and PP in cosmetic sample simultaneously with recoveries between 99.2 % and 104.8 %.Based on multi-templates molecularly imprinted technic, by adjusting the ratio between the template molecules, a MIPs sensor was developed to determine the total content of a group of homologous compounds as well as target compounds with different sort at the same time. This MIPs sensor was simpler to construct and operate, and provided an adequate sensitivity, good repeatability and acceptable selectivity. |
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