Identification of methamphetamines and over-the-counter sympathometic amines by full-scan GC-ion trap MS with electron impact and chemical ionization.

Abstract

Listen

Translate article

An underivatized methane chemical ionization (CI) assay for measuring amphetamines in urine was evaluated against derivatized electron impact (EI) assays using a gas chromatograph-ion trap mass spectrometer. The full-scan CI mass spectra of methamphetamine, ephedrine/pseudoephedrine, and phentermine were compared with the full scan and three-ion EI mass spectra of heptafluorobutyric anhydride (HFBA) and 4-carbethoxyhexafluorobutyryl chloride (CB) derivatives. The fragmentation patterns for these compounds were nearly identical for the three major high molecular weight ions (m/z 254, 210, and 169 for EI-HFBA derivatives, and m/z 308, 262, and 280 for EI-CB derivatives). The CI mass spectra of the underivatized drugs contained more discernible differences at the higher molecular weights, including m/z 119, 148, and 150 for methamphetamine, 148, 166, and 176 for ephedrine/pseudoephedrine, and 91, 133, and 150 for phentermine. The within-run precision ranged from 7-9% for CI versus 5-6% for EI with HFBA derivatization (mean 500 ng/mL, n = 5). The limits of detection (LOD) for amphetamine and methamphetamine were 2.4 and 8.6 ng/mL, respectively, for CI versus 0.7 and 1.4 ng/mL for EI. The limits of quantitation (LOQ) were 4.5 and 19.1 ng/mL for CI versus 1.4 and 5.7 ng/mL for EI. The use of full-scan mass spectral analysis with either electron impact or chemical ionization provides additional qualitative data that may be helpful for measuring methamphetamine in the presence of other sympathomimetic amines.