Voltammetric sensors based on gel composites containing carbon nanotubes and an ionic liquid

Possibilities of using electrode coatings based on a gel of carboxylated multiwall carbon nanotubes (MWCNTs) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIm]PF6) for the creation of a voltammetric sensor with electrocatalytic properties with respect to the pharmacological group of catecholamines—levodopa, methyldopa, and carbidopa—are considered. Using cyclic voltammetry, it was found that a glassy carbon electrode coated with a thin layer of an MWCNT–[BMIm]PF6 gel or an MWCNT–[BMIm]PF6–Nafion gel-composite induced a decrease in overvoltage (~60 mV), improved the reversibility of the redox reaction, and increased oxidation currents of the studied substances in comparison with an unmodified glassy carbon electrode. The concentration dependence of the analytical signal was linear in the ranges of 1–250, 2–350, and 5–400 mM for carbidopa, levodopa, and methyldopa, respectively. In the determination of the specified substances in diluted urine samples and tableted drugs, the accuracy index was 98–102% and the relative standard deviation, 0.3–5% (n = 5, P = 0.95).