Aim of our war was to investigate the degradation of diazinon in the model mixture in comparison with the experimental preparation. Methyl alcohol was used as a basis for the manufacture of diazinon drops and the model mixture. The concentration of diazinon was determined by reversed-phase high performance liquid chromatography on the third, fourteenth and twenty-first day after preparation of the model mixture and experimental preparation when stored at room temperature. Despite the large number of publications studying the degradation of diazinon under the influence of various factors, there is a need to study this process in mixtures of a specific composition, in particular in new veterinary drugs that have not yet been studied. This article presents the results of determining the content of diazinon in 10% of the drug and the model mixture based on methyl alcohol. The analyzes were performed on a Knauer liquid chromatograph with a spectrophotometric detector equipped with a Luna® Omega Polar C 18 150 × 4.6 mm column filled with a 5 μm particle sorbent from Phenomenex with a universal C 18 pre-column 4 × 3.0 mm ID. Mobile phase: degassed mixture of acetonitrile: water in the ratio 65:35, flow rate was 1.1 ml/min, temperature of the column was ambient. Diazinone was detected at 245 nm. Injection volume was 0.050 ml and the time of one separation – 20 minutes. The appearance of an unknown peak on the 3 min chromatogram of the solution of the production experimental preparation was revealed. On the twenty-first day of storage of the experimental drug, the content of diazinon decreased to 34 % of the stated amount. On the third and twenty-first day of storage of the model mixture, a decrease in the content of diazinon by 16 % and 79%, respectively, and the appearance of an additional peak were observed. The use of methyl alcohol with other components is likely to be a factor in the breakdown of diazinon in the drug. According to the recipe of the drug, methanol is about half the content of ingredients. This composition does not provide stability of the proposed dosage form of the drug. The next step will be to study the effect of other solvents on maintaining the stated concentration of diazinon.

The aim of the study was to investigate the stability of diazinon in two model mixtures in which the active substance content is 10%. Methyl and isopropyl alcohols were used as a basis for the production of model solutions with diazinon. According to the recipe of model drugs, methyl or isopropyl alcohols make up about half of the content of drug components. The diazinon content was determined by reversed-phase high performance liquid chromatography (HPLC) on 3, 14 and 21 days for the model mixture with methyl alcohol and on 14 and 50 days for the mixture with isopropyl alcohol. A significant number of publications have been devoted to the study of the degradation of diazinon and other nonspecific organophosphorus pesticides under the influence of various factors. However, it remains relevant to study this process in mixtures of a certain composition, in particular in new veterinary drugs under development. This article presents a comparison of the results of determination the content of diazinon in model mixtures based on methyl and isopropyl alcohols. The analyzes were performed on a Knauer liquid chromatograph with a spectrophotometric detector equipped with a Luna® Omega Polar C 18 150 × 4.6 mm column filled with a 5 μm sorbent of Phenomenex particle size with a 4 × 3.0 mm universal C 18 protective column. Mobile phase: degassed mixture of acetonitrile: water in the ratio 65:35, flow rate 1.1 ml / min at a column temperature of 20 °C, detection at a wavelength of 245 nm, injection volume - 0.050 ml, time of one separation - 20 minutes. It was found that the content of diazinon on the 21st day of storage of the model mixture based on methyl alcohol is about 30 % of the applied, while on the 50th day of storage of the model mixture based on isopropyl alcohol – 97 %. As we found in previous studies, the use of methyl alcohol is a probable factor in the breakdown of diazinon in the drug. The appearance of the peak of one of the products of diazinon for 3 min of the chromatogram of solutions of the production experimental preparation and the model mixture made in the HPLC laboratory with the solvent methanol was noted. When replacing methanol with isopropanol, the chromatogram of the drug solution did not show the appearance of an additional peak, except for the peak identified as diazinon. The use of isopropyl alcohol does not reduce the concentration of diazinon in the model mixture, as in the case of methanol. The composition with isopropyl alcohol provides relative stability of the model mixture.