Identification of functional groups in the ATR-FTIR spectra of 2C-X and DOX amphetamine analogues

Abstract

Amphetamine-type stimulants (ATS) and their ring-substituted analogues represent a major category of illicit substances that are under severe regulations in Europe and worldwide. Hence, the characterization and identification of ATS have a key role in law enforcement.

Currently, the automatic spectral identification is generally done by using a distance measure (e.g. the Euclidean distance) in order to find the best match in the available collection of known spectra. This approach is very useful when the spectrum of the analyzed sample is present in the spectral database of the computer connected to the analytical instrument. However, this computational method fails when the spectrum of the analyzed substance is not available in the spectral library. In this situation, the identification of the unknown must rely on the identification of the bands associated with the various types of vibrations of the chemical groups, which is a very tedious process.

In this paper we are presenting a Matlab script designed to automatically identify the presence of a variety of functional groups present in the molecular structure of the main 2C-x and DOx ATS, based on Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR). The position and intensity of the absorption bands associated to the functional groups specific to these hallucinogens have been identified by analyzing the ATR-FTIR spectra of 25 2C-x and DOx compounds. Once the main absorptions have been automatically attributed to the chemical groups present in the molecular structure of these ATS, the identification of an unknown not present in the database may be performed in a faster and much more reliable manner.