Gas chromatography with dual cold electron ionization mass spectrometry and vacuum ultraviolet detection for the analysis of phenylethylamine analogues

Abstract

Identification of phenethylamine (PEA) analogues is of great importance and requires analytical methods of high specificity. Forensic drug analysis is often performed by gas chromatography (GC) most commonly coupled with mass spectrometric (MS) detection. However, analysis of labile compounds is problematic with classical electron ionization (EI)-MS, and positional isomers may be difficult to differentiate by MS. Cold electron ionization (cold EI) improves molecular ion relative intensity by reducing the analyte vibrational energy prior to ionization. Vacuum ultraviolet (VUV) is a gas phase technique that can provide complementary selectivity to MS for identification. In this study, cold EI-MS was used in parallel with VUV detection for the analysis of select PEA analogues and positional isomers. Molecular ion relative intensity was increased for nearly all compounds included in this study. Principal component analysis demonstrated that VUV is more successful at distinguishing between positional isomers than MS. A library database of VUV spectra was set up to identify compounds, which was later used to deconvolute spectra of coeluting compounds. Detection limits for VUV are lower than those of MS with cold-EI, where VUV is capable of reaching sub-microgram per milliliter levels. Linearity tests on VUV showed high correlation coefficients (R2 > 0.999) for close to or over and order-of-magnitude dynamic range.