Methods of separation at the preparatory stage of criminal examination of material evidence

Abstract

In expert practice, questions often arise related to the separation (separation) of research objects from a mixture of dissimilar particles of solid materials, liquids of different densities, emulsions, two-phase media. During the study, physical and chemical separation methods are used. The choice of the separation method depends on the percentage composition and properties of the mixture and its constituent components. Expert research is carried out using various methods of separation: by mass (inertial), by size, electrical, magnetic, radiometric, photometric, etc. Chemical separation is its separate type. Analysis of expert practice indicates that separation is mainly applied during the forensic investigation of metals and alloys (solids), drugs (solids, liquid substances) and petroleum products (liquid substances). The article analyzes the methods of separation at the preparatory stage of the expert study of microparticles of precious metals and handicraft drugs. Forensic investigation of metal and alloy products is one of the most difficult, since the detection and separation of microparticles of the metal under study from other metal particles and their subsequent identification require the use of both chemical and instrumental research methods. The separation of the metal under study from the mixture of other metal particles was carried out by the method of mechanical and magnetic separation and chemical (selective dissolution) separation. During the expert study of acetylated opium using chromatographic methods, difficulties often arise associated with the separation of components due to the presence of a large amount of ballast substances (in particular, chlorophyll) extracted from poppy straw in acetylated opium. The use of an inertial separation method makes it possible to speed up the separation of an aqueous solution of a narcotic drug emulsion and an extracting organic solvent.