Electrooxidation of phenol was studied on platinum electrode in five aprotic non-aqueous solvents (acetonitrile, dimethyl sulfoxide, dimethyl formamide, acetone, and tetrahydrofuran) with cyclic and normal pulse voltammetry. The cyclic voltammetric results showed that fouling of the electrode surface by the polyphenol took place continuously in dimethyl formamide and a weak passivation of the electrode could be observed in dimethyl sulfoxide. From this solvent, a coherent and mechanically removable, weakly adsorbed layer could be obtained. In the other three solvents, the electrode passivated completely after five scans. Diffusion barrier properties of the polymer formed in acetone were the most pronounced of all solvents towards a redox probe. Normal pulse voltammetric investigations showed that the extent of electrode passivation is insignificant in three of the solvents used. It was due to the application of the short anodic potential pulses where the oxidation of phenol occurred and the formed oligomers diffused into the bulk of solution.

A new sensor for direct potentiometric determination of thiabendazole (TBZ) was prepared. The ionic pair of TBZ cation and the 5-sulfosalicylate anion was used as the new sensor material incorporated in liquid type of ion-selective electrode membrane for TBZ determination. For optimization of the membrane of the sensor for TBZ determination, six different plasticizers and the content of the sensor material in the membrane were varied. The chosen sensor with dibutyl sebacate (DS) as plasticizer and 1% of sensor material in the membrane was characterized with Nernstian response towards TBZ (62.2 mV/decade of activity), a wide working range (8.6∙10^-7-1.0∙10^-3 M), and a low limit of detection (3.2·10^-7 M). Also, it proved to be an accurate and reliable sensor for TBZ determination in pure and real samples (peel of oranges, lemons and bananas) where it was determined using direct potentiometry and Gran method.

In this work, the effects of the scan rate and the concentration of the substituted phenols on the peak currents or current plateaus have been investigated. Voltammetric curves recorded by a platinum microelectrode varied significantly under different experimental conditions in cases of 4-chlorophenol, 4-tert-butylphenol, and 4-nitrophenol. In the case of 4-methoxyphenol and 4-tert-butylphenol, when the experiments were performed in the lower concentration range in acetonitrile, the plateau current and peak current showed linear dependence on phenol concentration. Therefore, these ranges offer opportunity for further characterization. The electrode reaction of 4-methoxyphenol was found to be a diffusion-controlled process in the solvents applied (water, acetonitrile, dimethyl sulfoxide, dimethyl formamide, nitrobenzene, acetone, dichloromethane, methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol). Diffusion coefficients of 4-methoxyphenol were determined with a microelectrode using the steady-state voltammograms. Diffusion coefficients of other phenols were measured only in acetonitrile with a macroelectrode. In agreement with known theories, the diffusion coefficients showed inversely proportional relationships with the solvent viscosities. Special care was needed in 1-pentanol solvent since the increasing anodic peaks appeared after the first scan and overlaid with the sigmoidal-shaped regular microelectrode voltammograms. This observation is probably due to formation of adhering residual electroactive products.

The electropolymerization of three phenylphenol isomers was studied in methyl isobutyl ketone and mesityl oxide, and the remarkable differences highlighted the importance of the carbon–carbon double bond in mesityl oxide. In the case of each substrate, a brownish deposit formed during the electrooxidation. The obvious difference between the polymers formed from the two solvents was recognized via voltammetric signal enhancement of 4-methoxyphenol and 4-chlorophenol, and it was only observed in the case of mesityl oxide. The experiments highlighted that incorporation of a cavitand with biphenyl groups on the upper rim of the polymers of phenylphenols improved the results to a small extent. The cavitand was, itself, electroactive without any fouling effect. As 2-phenylphenol is by far the cheapest of the three isomers, a cavitand was incorporated into its polymer, which was exploited to solve analytical problems while mesityl oxide was used as solvent. Useful quantifications were achieved in organic solvents; however, it failed under aqueous conditions due to the high hydrophobicity of the deposit. Application of differential pulse voltammetry for 4-methoxyphenol and 4-chlorophenol gave detection limits of 9.28 and 50.8 μM in acetonitrile, respectively. This procedure resulted in the immobilization of cavitand derivatives onto the electrode’s surface, and the layer formed offered selective sensing of phenols by electrochemical methods.

The two naphthol isomers were investigated in different organic solvents by taking cyclic voltammograms, and fouling took place on a platinum electrode surface, except for dimethyl sulfoxide and dimethyl formamide. Studies in allyl alcohol rarely used in electrochemical investigations pointed to the importance of the carbon–carbon double bond as electrode deactivation was remarkably faster compared with its saturated analog solvent. Similarly, the use of the other unsaturated solvent mesityl oxide in the electropolymerization of naphthols resulted in different findings compared with methyl isobutyl ketone. As dimethyl formamide was the best choice concerning the solubility of products, it was successfully tested in electrode renewal after deactivation in an aqueous solution. The increase in dimethyl formamide content led to more and more improved reproducibility of the currents of the outlined aromatic compounds. Naphthol isomers were assessed in the suppression of layer growth originating from the electrooxidation of another monomer phloroglucinol. Its simultaneous electrooxidation with naphthol monomers had a dramatic effect on layer morphology and it was found that instead of a coherent organic layer originating from the homopolymerization of phloroglucinol, the copolymerization with naphthols led to the development of more porous and rougher deposits. The suppressed electropolymerization thus increased sensitivity towards a chosen redox active compound, 4-methoxyphenol.