Volume 42, Issue 1 (January 1997)
Distinguishing Amphetamine, Methamphetamine and 3,4-Methylenedioxymethamphetamine from Other Sympathomimetic Amines After Rapid Derivatization with Propyl Chloroformate and Analysis by Gas Chromatography—Chemical Ionization Mass Spectrometry
Misidentification of ephedrine and pseudoephedrine as methamphetamine has been reported because of similar retention times of their derivatives in gas chromatography as well as very similar mass spectral fragmentation patterns in the conventional electron impact mode of analysis. Recently, a new derivatization of amphetamine and methamphetamine has been described using propyl chloroformate. The derivatization is easily accomplished at room temperature by adding the derivatizing reagent in the extraction solvent because the reagent is stable in the presence of water. The electron impact mass spectrum of derivatized methamphetamine (base peak, m/z 144, other peaks at m/z 102, 58) is similar to the electron impact mass spectrum of both derivatized pseudoephedrine (base peak, m/z 144, other peaks, m/z 102, 58), and ephedrine (base peak, m/z 144, other peaks, m/z 102, 58). Therefore, misidentification of ephedrine and pseudoephedrine as methamphetamine is possible even if this new derivatization technique is used with conventional gas chromatography/electron impact mass spectrometry. We demonstrated that by using chemical ionization mass spectrometry, this problem can be eliminated. In the chemical ionization, using methane as a reagent gas, derivatized methamphetamine showed a protonated molecular ion as a base peak at m/z 236 and other strong peaks at m/z 144 and 119, both derivatized ephedrine and pseudoephedrine showed a base peak at m/z 192 and another strong peak at m/z 148, thus differentiating them clearly from methamphetamine. Amphetamine also showed a protonated molecular ion at m/z 222 and other strong peaks at m/z 130 and 119, whereas phenylpropanolamine after derivatization with propyl chloroformate showed a base peak at m/z 220 and another strong peak at m/z 238, thus differentiating it from amphetamine. The designer drug 3,4-methylenedioxymethamphetamine (MDMA) showed a molecular ion at m/z 279 using electron impact, after derivatization with propyl chloroformate. Using chemical ionization, a relatively stronger protonated molecular ion at m/z 280 was observed. We conclude that using chemical ionization instead of conventional electron impact and propyl chloroformate derivatization, misidentification of ephedrine or pseudoephedrine as methamphetamine or phenylpropanolamine as amphetamine can be eliminated.