Identification of zopiclone in forensic evidence by chemical and optical methods

The study of potent drugs, in particular zopiclone, is common in the practice of the Expert Service units of the Ministry of Internal Affairs of Ukraine. In order to ensure reliable identification and, subsequently, accurate quantitative determination of controlled compounds, analysis schemes are being developed that involve the application of comprehensive analytical methods in a clear logical sequence. The aim of the present study was to systematize the available analytical methods for zopiclone identification in various matrices and to develop an optimized identification protocol using chemical reactions and optical methods. In this work, zopiclone substance and tablets registered in Ukraine were used. The identification of the compound was carried out using chemical reactions and physicochemical methods, including infrared spectroscopy and ultraviolet spectrophotometry. As the objects submitted for forensic analysis may contain zopiclone along with various impurities and excipients, a preliminary purification step by chloroform extraction was performed. For identification purposes, chemical and optical analytical methods are proposed. The analysis should begin with commonly accepted precipitation and color reactions, and specific color reactions are further proposed: with N,Ndimethylaminobenzaldehyde or vanillin in concentrated H₂SO₄; perhydrolysis-based reactions with H₂O₂ in alkaline media (using ethanolic solutions of 3,3′,5,5′-tetramethylbenzidine, benzidine, o-phenylenediamine, and indole); or alkaline hydrolysis-based reactions (using 2,4-dinitrophenylhydrazine, benzidine, o-phenylenediamine, o-toluidine, and hydroxylamine in the presence of FeCl₃). Next, identification should be confirmed by ultraviolet or infrared spectroscopy methods: zopiclone has a distinct absorption maximum at 304.0 nm, while its IR spectrum is characterised by the following absorption bands: 1728.536, 1711.739, 1577.579, 1564.627, 1460.424, 1415.180, 1367.423, and 1083.699 cm⁻¹. We propose to use UV spectrophotometry (calibration curve method at a wavelength of 304.0 nm) and IR spectroscopy (using chloroform as a solvent, with the measurement of the absorption band areas to be performed in the 1650–1750 cm⁻¹ stretching vibration region) for the quantitative determination of zopiclone. Consequently, the proposed schemes for the identification and quantitative assay of zopiclone using chemical reactions and optical methods, the implementation of which into the practical activities of a forensic expert allows for the formation of scientifically based and objective conclusions.