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Formation of Trifluoroacetylated Ephedrine During the Analysis of a Pseudoephedrine-Formaldehyde Adduct by TFAA Derivatization Followed by GC-MS

NCJ Number
Journal of Forensic Sciences Volume: 54 Issue: 2 Dated: March 2009 Pages: 365-369
Ahmad F. Lim bin Abdullah Ph.D.; Gordon M. Miskelly Ph.D.
Date Published
March 2009
5 pages
This paper describes the procedures for the derivatization of pseudoephedrine (a common precursor for the preparation of S-methamphetamine) prior to trace analysis by gas chromatography-mass spectrometry (GC-MS) when investigating the compositions of chemicals from clandestine methamphetamine laboratories.
The derivatization of pseudoephedrine prior to trace analysis by GC-MS is desirable for two reasons. First, underivatized pseudoephedrine gives tailing peaks on common GC-MS columns, making peak integration difficult, leading to a high limit of detection for underivatized pseudoephedrine. Second, the base peak in the mass spectrum of pseudoephedrine is at m/z 58 with no major peaks at m/z >91, a pattern that is also seen for other amines such as methamphetamine and phentermine. Appropriate derivatization can provide improved separation and more discriminatory mass spectra. Analysis of underivatized pseudoephedrine and pseudoephedrine is possible for bulk samples; however, it is not suitable for trace samples, since it is too insensitive and is susceptible to formation of impurities such as the oxazolidines formed from pseudoephedrine in the presence of carbonyl compounds. Trifluoroacetic acid anhydride (TFAA) derivatization of pseudoephedrine forms N,O-bis(trifluoroacetyl) pseudoephedrine and also N-mono-trifluoroacetyl pseudoephedrine in the case of incomplete derivatization. In the presence of formaldehyde, pseudoephedrine forms (4S,5S)-3,4-dimethyl-5-phenyloxazodine. Upon reaction with TFAA, this compound forms N,O-bis(trifluoroacetyl)pseudoephedrine, but N-mono-trifluoroacetyl pseudoephedrine is also detected even when TFAA is in excess and extended reaction times are used. In addition, variable amounts of N,O-bis(trifluoroacetyl)ephedrine are also observed, which results from epimerization during the derivatization and analysis process; therefore, care must be taken when interpreting TFAA-derivatized pseudoephedrine or ephedrine GC-MS chromatograms if formaldehyde contamination is possible. 5 figures and 20 references