Molecularly imprinted polymers (MIPs) for bisphenol A (BPA) were prepared by two synthetic routes: semi-covalent and noncovalent methodology. The molecular imprinting effect was evaluated using the polymers in HPLC and SPE. Polymers prepared with noncovalent mode were proven more effective. These polymers were applied in SPE facilitating selective retention of BPA from bottled water and milk. The developed sample preparation was simple and efficient comprising only dilution of milk and MISPE prior to LC-MS analysis. Overall MISPE enhanced sample clean-up. Compared with control nonimprinted polymers and conventional C18 SPE cartridges, the MIPs exhibited selective analyte recognition. The method provided quantitative BPA recoveries, very good reproducibility (% RSDs lower than 7%), and low LOD (0.2 ng/g). MIP interacts similarly with deuterated BPA allowing its use as internal standard in LC-MS. The most critical parameters of MISPE were the organic content in loading-washing medium and the washing volume. Low flow rates in the elution step enhanced extraction recovery. Important advantages of the MIP were: the high breakthrough volumes (> 500 mL of water), high mass capacity (> 10 ng/mg of MIP sorbent), good linearity, and good stability in performance for over 35 cycles of use.

The electrochemical behavior and thermal stability of double stranded oligonucleotides containing 5-methyl-cytosine and 7-deaza-guanosine as nucleotide analogues, as well as of Jurkat genomic DNAs methylated to different degree were studied by ACV and SWV and by thernal denaturation analysis. ACV and SWV combined with thermal denaturation analysis of the natural and modified oligonucleotides gave information regarding the presence of methylation and the concomitant conformational changes. ACV and SWV of Jurkat DNA mixtures methylated to different degrees revealed a decrease of the peak heights with increasing methylation, indicating an increase of structural rigidity, in agreement with the thermal denaturation data. These results verify the, possibly local, conformational changes introduced by DNA methylation. The results obtained in all cases were reproducible.

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Proflavine binds with DNA in a complicated manner. This work involves the electrochemical study of this interaction using differential pulse voltammetry at a carbon paste electrode (CPE) and alternating current voltammetry at a hanging mercury drop electrode (HMDE). At the CPE the peak current intensity at 1.0 V (corresponding to the oxidation of the guanine residues) decreased by increasing the concentration of proflavine. At the HMDE, a decrease in the current intensity of the DNA peak at À1.2 V (corresponding to segmental desorption) was also observed by increasing the concentration of proflavine. These results confirmed, electrochemically, that proflavine intercalates within the DNA double helix and changes its conformation.

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