Vol 79, No 6 (2024)

The development of chemical sensor devices operating in non-contact mode is of primary interest due to the demand from various industries for a fast, simple and inexpensive determination of chemical composition in different media in a non-invasive way. One of the promising directions for the development of analytical devices with such characteristics is the use of high-frequency electrical signals. The paper discusses the evolution of high-frequency contactless conductometry method, likewise other methods and devices operating on similar physical principles (dielectric spectroscopy, microwave sensors, C4D detectors).

Hydroxyl radical is the most aggressive and dangerous product of incomplete reduction of oxygen in the body, therefore its determination and the influence of various antioxidants on the inhibition of OH-radicals is an urgent task. An impedance-metric sensor for the determination of hydroxyl radicals based on a graphite electrode modified with electrochemically deposited gold and self-organizing monolayer of N-acetyl-L-cysteine (ACC) has been proposed. The use of ACC causes high selectivity of the sensor, and the use of non-Faraday impedance as a method of analytical signal registration allows to reach the detection limit of OH-radicals of 0.01 nM with a linear range of detectable concentrations of 0.08-8 nM. The developed sensor has been successfully applied to evaluate the activity of some antioxidants (ascorbic acid, glutathione, coenzyme Q10) in relation to OH-radicals.

For selective determination of the antibiotic clarithromycin, a voltammetric sensor based on a glass-carbon electrode modified with a composite of chitosan, Carboblack C graphitized carbon black and polyarylenephthalide containing diphenylene-thio- and diphenylene oxide fragments in the main chain of the polymer in the ratio of 1 : 2 with molecular imprints of clarithromycin obtained by phase inversion method was developed. The composition and morphology of the modifying coating were studied using IR spectroscopy and scanning electron microscopy. The electrochemical and analytical characteristics of the sensor were studied by electrochemical impedance spectroscopy, cyclic and differential-pulse voltammetry. Optimal conditions for analytical signal registration were selected. Using [Fe(CN) ]₆^3−/4− as a probe, the linear range of determined concentrations was 1 × 10^-7 -5 × 10^-4 M with a detection limit of 5.3 × 10^-8 M. It is shown that the use of a polymer with molecular imprints of clarithromycin increases the sensitivity of the sensor almost 10 times compared to the non-imprinted polymer. The proposed sensor was tested on samples of urine, blood plasma, as well as food products (meat, milk), the degree of extraction was 90-96, 80 and 92%, respectively, and the relative standard deviation did not exceed 10% in all cases.

To recognize and determine the enantiomers of clopidogrel, a sensor system based on a glassy carbon electrode modified with Carbopack X mesoporous carbon black and cyclopentadiene derivatives – (1S)-2-cyclopenta-2,4-dien-1-yl-1,7,7-trimethylbicyclo[2.2.1]heptane; (1S, 2S, 4R)-2-cyclopenta-1,3-dien-1-yl-1-isopropyl-4-methylcyclohexane; 9-[(1S,2S,5R)-2-isopropyl-5-methylcyclohexyl]-9H-fluorene. Due to the unique properties of Carbopack X, such as large surface area and high conductivity, it was possible to obtain a mechanically stable and sensitive sensor layer that firmly retains chiral selector molecules on its surface. The morphological, electrochemical and analytical properties of the obtained sensors were studied by scanning electron microscopy, electrochemical impedance spectroscopy, cyclic and differential pulse voltammetry. The determination of clopidogrel enantiomers in biological fluids has been carried out; linear dependences of oxidation peak currents on their concentration in solution for all sensors are preserved in the concentration range from 1 × 10^–6 to 5 × 10^–4 M. The sensors are cross-sensitized, which allowed combining them into a sensor system with high enantioselectivity and sensitivity towards clopidogrel enantiomers. With the proposed sensor system, the probability of correctly recognizing samples increases compared to single sensors. In all cases, the content of R-clopidogrel in the mixture is correctly determined with a relative error not exceeding 9% and a degree of discovery ranging from 96 to 102%.

Abstract. It was found that mixed valent iridium oxides electrodeposited on the surface of a glass-carbon electrode exhibit catalytic activity in the oxidation of caffeine. A more pronounced catalytic effect was obtained on the electrode modified with a composite based on a film of perfluorinated sulfonated polymer (Nafion) and mixed valent iridium oxides. A selective voltammetric method for the determination of caffeine was developed. A linear logarithmic dependence of current on caffeine concentration was observed in the range from 1×10^–8 to 5×10^–3 M. The developed method was used in the determination of caffeine in energy drinks.

The sodium salt of 3-nitro-4-hydroxy-7-methylthio-4H-[1,2,4]triazolo[5,1-c][1,2,4]triazinide monohydrate (compound (1)) is one of the promising compounds that showed potential antiviral activity against Coxsackie B3 virus. It was established by cyclic voltammetry that the electrochemical activity of compound 1 on a glass-carbon electrode in Britton-Robbinson buffer solution (BBR) is due to the electroreduction of the nitro group. A method for the determination of compound 1 by direct cathodic square-wave voltammetry was developed. The linearity area of the graduation plot using the developed method in BBR solution (pH 2.0 ± ٠.١) is 10-300 mg/L (R² = 0.999) with detection and determination limits of 1.27 and 4.11 mg/L, respectively.

A non-destructive method for analyzing medicinal products (non-steroidal anti-inflammatory drugs, fluoroquinolones, acetylsalicylic acid, vinpocetine, tetracyclines) based on diffuse reflection of IR radiation using a smartphone and a device printed on a 3D printer is proposed. It was established that the diffuse reflection of IR radiation (850 nm) from tabletized medicinal products can be recorded using a smartphone camera. Blister packaging and tablet coating slightly reduce the intensity of the diffuse light reflection signal at a wavelength of 850 nm, as confirmed by a comparative analysis of colorimetric measurement results in medicinal product samples inside the packaging, outside the packaging, and on tablet fractures. A correlation between the analytical signal and the concentration of the active substance is observed regardless of the study variant. The data array was processed using principal component analysis (PCA), hierarchical cluster analysis (HCA), partial least squares regression (PLS), and least squares methods using PhotoMetrix PRO® software for smartphones. It is shown that these algorithms can identify drugs by their manufacturer and determine the concentration of active ingredients. The colorimetric signals from tablets of a single manufacturer form separate clusters on dendrograms created using the HCA algorithm. Data obtained using PCA indicate the location of signals from tablets of different manufacturers in separate quadrants, facilitating the identification of the pharmaceutical company. The use of chemometric analysis methods for determining the concentration of the active substance is considered.