Determination of active substances of the class of sulphonyl urea in matrixes

Abstract

Goal. Selection of chromatographic method and development of a method for controlling the content of active substances nicosulfuron, rimsulfuron and thifensulfuron-methyl separately and in a combined presence in different combinations in matrices (formulations).
 Methods. The active substances were determined by thin layer chromatography (TLC). The linear range of the dependence of the area of the chromatographic zones on the amount of active substance was estimated by statistical methods using correlation-regression analysis.
 Results. Determination of pesticides includes the main stages: characterization of active substances by polarity; extraction their from the analyzed matrix; chromatographic separation, detection and quantification. The limiting integral indicator in the analysis is the dipole moment (µ, D), which characterizes the polarity of the compounds and their physicochemical properties. Nicosulfuron, rimsulfuron and thifensulfuron-methyl are low-polar compounds (2 <µ ≤ 6, D) with dipole moments of 5.48; 5.30 and 5.28 D, respectively. Extraction of active substances is carried out with ethanol. Qualitative determination — in a thin layer of adsorbent silica gel in the mobile phase (hexane + chloroform + ethanol + ethanoic acid 30:10:5:1) and with a dielectric constant ε = 5.12. Compounds were identified under a chromatoscope (λ 254 nm) and using bromophenol blue developing reagent and subsequent bleaching of the chromatogram background with citric acid solution. The dependence of the area of the chromatographic zone of the compound (S, mm2) on its amount (C, µg) is linear in the detection range of 0.30—1.30 µg and is described by the regression equation for: thifensulfuron-methyl S = 25.057 C + 0.4367 (R2 = 1.00); nicosulfuron S = 22.272 C + 0.0532 (R2 = 1.00); rimsulfuron S = 17.519 C + 0.9456 (R2 = 1.00). The equations are used to quantify the active substances on the chromatogram.
 Conclusions. The use of TLC method allows to select selective conditions and to develop a method for determination of thifensulfuron-methyl, nicosulfuron and rimsulfuron in herbicide formulations separately and in combined presence in different combinations and quantities, which allows to determine three active substances in one analysis with high accuracy reproducibility (relative error, <5% at n = 5, P = 0.95). The introduction of the developed and patented method makes it possible to determine the active substances of the sulfonylurea class in herbicide formulations by analytical and toxicological laboratories, testing services without the use of expensive devices.