These plants are widely used as spices for cooking and can be considered one of the sources of antioxidants in human diet. Furthermore, isopropylmethylphenols have antibacterial, antifungal, insecticidal, and anti-oxidative properties [2; 3; 4], promoting the wide use of these compounds in the cosmetic, food, and pharmaceutical industries. Thus, the control of isopropylphenols concentration in real samples is of practical interest. Isopropylmethylphenols are electrochemically active and detectable using electrochemical methods. Nevertheless, thymol and carvacrol are less studied in comparison to other natural phenolics. Being isomers, both compounds are oxidized at almost the same potentials. Therefore, total isopropylmethylphenols contents are usually quantified. Sensitive voltammetric methods for the isopropylmethylphenols quantification have been developed using chemically modified electrodes. Multi-walled carbon nanotubes (MWNTs) and their layer-by-layer combination with electropolymerized thymolphthalein  
Figure 20: Immobilization of specific probes and triplex formation between ds-DNA of HBV and PL, P2 probes. have been used as electrode surface modifiers. Application of MWNTs significantly increases the effective surface area and conductivity. Polymeric film provides structural similarity to the analytes and the porous structure, leading to the increase in the determination sensitivity. The surface of the electrodes has been characterized with SEM, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). SEM data confirm successful immobilization of the modifiers. According to the electrochemical data, the effective surface area of modified electrodes is significantly increased in comparison to GCE. The EIS data show a statistically significant decrease in the charge transfer resistance for the modified electrodes vs. GCE. Thymol and carvacrol electrooxidation parameters on the electrodes developed have been found, and corresponding oxidation schemes have been suggested. Differential pulse voltammetry has been applied for the quantification of isopropylmethylphenols. The analytical characteristics obtained are improved in comparison to those reported earlier for other modified electrodes. The selectivity of isopropylmethylphenols response in the presence of typical interferences and other natural phenolics is an important advantage of the methods developed. The analytical capabilities of the methods have been successfully shown on example of oregano and thyme spices. Validation to independent method has been performed. Thus, the approaches developed are simple, reliable, cost-effective, and can be applied for the routine analysis for the fast screening of the plant materials. ## References  
* [1] Ziyatdinova, G.K.; Budnikov, H.C. Spice antioxidants as objects of analytical chemistry. _J. Anal. Chem._**2018**, _73_, 946-965. * [2] Kachur, K.; Suntres, Z. The antibacterial properties of phenolic isomers, carvacrol and thymol. _Crit. Rev. Food Sci. Nutr._**2020**, _60_, 3042-3053. * [3] Ziyatdinova, G.; Budnikov, H. MWNT-based electrode for the voltammetric quantification of carvacrol. _Food Anal. Methods_**2021**, _14_, 401-410. * [4] Fachini-Queiroz, F.C. ; Kummer, R.; Estevao-Silva, C.F. ; Carvalho, M.D.d. ; Cunha, J.M. ; Grespan, R.; Bersani-Amado, C.A. ; Cuman, R.K.N. Effects of thymol and carvacrol, constituents of _Thymus vulgaris_ L. essential oil, on the inflammatory response. _Evid. Based Complement. Altern. Med._**2012**, _2012_, 657026. * [5]_14.5.