The Origin of a ‘Ghost’ Peak in the Gas Chromatography of Certain Intact Amine Salts and the Potential Scope and Analytical Value of the Phenomenon Causing the Peak

Abstract

When certain amine salts are subjected directly to gas chromatography (i.e., without prior derivatization or deprotonation) even when highly pure two or more peaks are observed, only one of which is due to elution of the amine freebase. These unexpected results are confusing to analysts and if inexplicable results such as these are presented as evidence in a court of law they erode confidence in forensic analysis. There is little discussion in the literature regarding the origins of one of the unexpected ‘ghost’ peaks. This article indicates that the particular ‘ghost’ peak under discussion is not a ghost at all, but a peak due to the analyte itself—it arises as a result of elution of intact amine salt or carry-over of a salt from a previous injection. Elution of HI or HBr amine salts using gas chromatography—mass spectrometry can readily be confirmed by searching for the presence of halide⁺ and hydrohalide⁺ ions, but confirmation of HCl salts requires the mass spectrometer’s scan range to commence at low m/z in order to avert analytical confusion. Certain amine salts, such as drugs and explosives, are very important in forensic chemistry and the development of methodology based upon gas chromatography for the analysis of these compounds in their intact salt forms (i.e., where the cation and anion pairing information is not lost) would be a valuable contribution to the field. Other fields of analytical chemistry, such as environmental monitoring and analysis of food and industrial products may also benefit from the development of a GC method for the analysis of intact amine salts. The results presented here suggest that further development of gas chromatography for the analysis of intact amine salts is warranted.