Abstract:

Surfactants are key compounds in agrochemical products that ensure properties such as viscosity, dispersity or homogeneity and are assisting the homogenous distribution of the active ingredient(s) over the target crop or promoting its uptake by the plant. There is limited knowledge, however, about the influence of by-products and impurities in a technical surfactant on the properties of the final product. In this context commercial available products of sodium bis(2-ethylhexyl) sulfosuccinate (AOT; anionic) and tristyrylphenol ethoxylates with an average number of 16 ethylene oxide units (TSP-16-ethoxylates; nonionic) - commonly used surfactants in agrochemical products - were investigated for their content of by-products. The by-products investigated for AOT were its isomeric surface-active mono-esterified sulfosuccinates. An analytical method based on liquid chromatography coupled to time of flight mass spectrometry (LC-ToF-MS) with exact mass measurement was developed to quantify main and by-products in AOT-product. An isomer-selective synthesis for both monoesters was developed for validation of the developed method. Significant differences were observed regarding the content of monoesters among four different suppliers and qualities of AOT-product. A storage stability test performed with a model agrochemical formulation using AOT-product showed decreasing dispersion stability with raised initial content of monoesters. The differences in monoester content were then used for product identification. This could be utilized as additional tool in detection of counterfeit products, as the supplier of the AOT-product in the original agrochemical product is known a priory. TSP-16-ethoylates were analytically characterized by quantifying all major styrenated ethoxylates against an internal standard using targeted LC-ToF-MS with exact mass measurement in combination with multivariate data analysis. Four suppliers and qualities were analyzed and compared with regard to their content of these styrenated ethoxylates. Significant differences were found between the suppliers based on the content of mono- and tetrastyrylphenol ethoxylates and mono- and distyrylphenol copolymerized propoxylates-ethoxylates, which were successfully utilized for supplier identification. Analytical characterization and control of surfactants may be a useful tool to avoid unwanted property changes in complex mixtures such as agrochemical products. Moreover, small variations in the composition of surfactants offer further opportunities for identification of counterfeit products. Future investigations could address the mode of action leading to raised sedimentation in an agrochemical product using AOT with raised content of monoesters. Furthermore, it should be investigated if the method developed for the characterization of TSP-16-ethoxylatesylates can be adapted to other ethoxylated surfactants and analytes with a comparably broad composition of main and by-products.