GC-IRD Analysis of Regioisomeric Substituted Phenethylamines of Mass Spectral Equivalence

The value of gas chromatography with vapor phase infrared spectrophotometric detection is described for a series of isomeric phenethylamines. The major mass spectral fragments for these unique isomers occur at equivalent mass and members of each series have equal molecular weights. The infrared spectra for these compounds allow for identification of any one of these amines to the exclusion of all other isomers of the series. This differentiation is accomplished without the need for chemical derivatization. All the studied regioisomers could be differentiated from the controlled drug substance via their vapor phase IR spectra. Capillary gas chromatography successfully resolved the side chain and ring regioisomers for those isomers included in this study.

Introduction:
Infrared spectroscopy is considered a confirmation method for the identification of organic compounds due to the uniqueness of infrared spectra for very similar organic molecules. Gas chromatography with infrared
detection (GC-IRD) is characterized by scanning quickly enough to obtain IR spectra of peaks eluting directly from capillary GC columns and the technique is not affected by polymorphism since the infrared spectra are obtained in the vapor phase. Thus this analytical method combines the separation power of GC with the identification power of IR. In this brief overview discussion we will focus on some example applications in the analysis of closely related compounds (regioisomers) often encountered in forensic drug chemistry.