Application of a new electrochemical sensor for voltammetric determination of p-nitrophenol and betulin

A highly sensitive electrochemical sensor based on a Surface Active Modifier (SAM) consisting of Taunit-M carbon nanotubes and mesoporous carbon (NanoTechCenter LLC, Tambov, Russia) is developed for the voltammetric determination of betulin and p-nitrophenol. The effect of the modifier concentration on the electrode surface on the analytical signal of betulin was studied, and a method for modifying the surface of the SAM graphite electrode was developed. The developed method is easy to use, fast, stable, sensitive, and cost-effective procedure, which can be used to detect these analytes in real samples. Voltammograms of p-nitrophenol were obtained for the first time on the developed modified electrochemical sensor and the dependence of the height of its analytical signal on the pH of a phosphate buffer thus obtained was studied in a wide pH range from 4 to 12, a background electrolyte with optimal pH was also chosen. Proceeding from the calibration dependences of the height of the betulin analytical signal on the concentration obtained for various background electrolytes with different pH and cation-anion composition, a background electrolyte with the maximum sensitivity of the analytical signal was selected on a modified electrochemical sensor. Study of cyclic voltammograms was carried out to understand the electrode processes, exhibiting a pronounced peak of anodic oxidation observed in a potential range from 0.7 to 0.9 V. However, there was no peak in the cathodic direction which indicates the irreversible nature of the electrode process. When determining the nature of currents, the Semerano criterion equal to 1.6 was calculated, which indicates the absence of the contribution of the diffusion component of the current. Verification of the correctness of the voltammetric method for determining betulin on a new  electrochemical sensor was carried out using the «spike-test» method. The data obtained show that the voltammetric determination of betulin can be carried out with a measurement error not exceeding 15%. The proposed modified electrodes were compared with previously known electrodes for the determination of pentacyclic triterpenoids and pesticides at concentrations of 0.5 × 10–3 – 8.0 × 10–3 mg/dm3.