The pharmaceutical industry is one of the most regulated industries in the world, and most medicines remain safe and effective. The level of impurity and degradation products in active pharmaceutical ingredients (APIs) must be strictly controlled and meet the specifications required by international bodies. for many years, chromatography has been the method of choice for assessing the chemical purity of medicinal substances and products and has a wide range of applications in the pharmaceutical industry, from research and development to laboratory quality control. The ability to integrate mass spectrometry into the chromatography workflow has been a real breakthrough in the science of separation, finding many inscriptions, especially in the field of pharmaceutical analysis. Therefore, the relevance of the research lies in finding the quantity of the composition of the created mixture – ear drops “Melavet” by the HPLC method with mass detection of the initial components. The purpose of the work is to create analytical methods for determining the active components of the mixture when they are present in the sample and interact with each other. Materials and methods: Chromato-mass-spectrometric studies, high-performance liquid chromatography (HPLC, LCMS). LCMS device: Agilent 1200 Quaternary DAD HPLC System (degasser, binary pump, autosampler, column thermostat, diode-matrix detector; single-quadrupole mass spectrometer Agilent 1100 LCMSD SL instrument; OpenLAB CDS Software. For the new combined veterinary test of ear drops “Melavet” 10 ml, containing various components, it is necessary to develop optimal methods of standardization. For this, 6 solutions of the external standard of each component were prepared. Based on the research, a method was developed for the simultaneous determination of the components in the model mixture ear drops “Melavet” 10 ml by the method of high-performance liquid chromatography using the same mobile and stationary phases, as well as similar chromatographic conditions, which were used during the study of individual samples of the external standard. When analyzing the chromatographic data, the presence of dioxidin in the mixture was fully consistent. In comparison with the external standards of each component, there are separate icons of substances on the chromatogram of the mixture, which contain information about the purity of the components and the interaction between them. During the research, a highly sensitive technique for the simultaneous determination of the components of the model mixture “Melavet” ear drops 10 ml by the method of high-performance liquid chromatography was developed. The optimal conditions for the simultaneous determination of the components of the mixture in one sample are selected. It was established that there is no interaction between the components of the mixture when they are simultaneously in the sample solution.