Comparison of GC–MS and GC–IRD methods for the differentiation of methamphetamine and regioisomeric substances

Gas chromatography–mass spectrometry (GC–MS) and gas chromatography–infrared detection (GC–IRD) methods were developed and compared for the differentiation of regioisomeric phenethylamines related to methamphetamine. There are a total of five regioisomeric phenethylamines (methamphetamine and four regioisomers) that produce essentially equivalent mass spectra. This unique set of five phenethylamines having the same molecular weight and elemental composition yield major mass spectral fragments at equivalent mass. The trifluoroacetyl derivatives of the primary and secondary amines yield characteristic individual fragment ions allowing structural differentiation among these regioisomers. The vapor phase infrared spectra generated via capillary gas chromatography differentiated among these compounds without the need for derivatization. The regioisomeric phenethylamines are well resolved by GC with the elution order generally determined by the degree of molecular linearity.