Identification and characterization of chemically masked derivatives of pseudoephedrine, ephedrine, methamphetamine,...

The emergence of chemically masked illicit drugs represents a challenge to global initiatives that are working to prevent their manufacture and distribution. Targeted analytical techniques currently used by law enforcement to identify unknown materials rely on spectroscopic and spectrophotometric databases that do not currently include some of these compounds, making their identification challenging. This study aimed to update compound spectral libraries to aid in the rapid detection and identification of these masked drugs, as well as to provide insight into their synthetic procedures. Five commonly employed protecting groups, acetyl, p-tosyl, methoxycarbonyl, Fmoc, and t-Boc, were appended to pseudoephedrine, ephedrine, methamphetamine, and MDMA. Characterization was carried out using NMR, GC-MS, FTIR, high-resolution LC-MS/MS, and common screening color tests. Some of the methoxycarbonyl and t-Boc derivatives and all of the Fmoc derivatives showed partial or full thermal degradation or rearrangement during GC-MS analysis, while LC-MS/MS analysis did not always show characteristic fragmentation that would allow unambiguous assignment of the structure. Restricted rotation in some of the derivatives meant that NMR assignments could only be made using NMR spectra acquired at elevated temperature. Therefore, GC-MS and LC-MS/MS analyses serve complementary roles for these derivatives, with NMR providing confirmation of structure for the pure materials if necessary.