Spectral Trends in GC-EI-MS Data Obtained from the SWGDRUG Library and Literature: A Resource for the Identification of Unknown Compounds

Rapid identification of new or emerging psychoactive substances remains a critical challenge in forensic drug chemistry laboratories. Current analytical protocols are well-designed for confirmation of known substances yet struggle when new compounds are encountered. Many laboratories initially attempt to classify new compounds using gas chromatography mass spectrometry (GC-MS) data. Though there is a large body of research focused on analysis of illicit substances with GC-MS, there is little high-level discussion of mass spectral trends for different classes of drugs. This manuscript compiles literature information and performs simple exploratory analyses on evaluated GC-MS data to investigate trends of electron ionization (EI) mass spectra on the most reported illicit substance classes. Additionally, this work offers other important aspects: brief discussions of how each class of drugs is used; descriptions of proposed fragmentation pathways of commonly observed ions in EI-MS data; and summaries of mass spectral trends that can help an analyst classify new illicit compounds.