Structure Analysis of the Interfering Substance N-methyl-2-phenylpropan-1-amine of Methamphetamine in Wastewater

Abstract

ObjectiveTo analyze the chemical structure of the interfering substance that affects the result of methamphetamine analysis in wastewater.MethodsA combination of GC-MS and liquid chromatography-quadrupole time-of-flight mass spectrometry （LC-QTOF-MS） was used to analyze the mass spectrum characteristics of the interfering substance that affects the result of methamphetamine analysis and to infer its possible structure. Liquid chromatography-triple quadrupole-mass spectrometry （LC-TQ-MS） was used to confirm the control material.ResultsUsing LC-QTOF-MS in positive electrospray ionization （ESI+） mode, the mass-to-charge ratio （m/z） of quasi-molecular ion in the MS1 mass spectrometry of interfering substance was identical to that of methamphetamine, indicating that the interfering substance was probably an isomer of methamphetamine. The MS2 mass spectra obtained at three collision energies of 15 V, 30 V and 45 V were highly similar to methamphetamine, suggesting that the interfering substance contained methylamino and benzyl groups. Further analysis using GC-MS in electron impact （EI） ionization mode showed that the base peak in the mass spectrum of the interfering substance was at m/z 44. The interfering substance was confirmed to be N-methyl-2-phenylpropan-1-amine by compared with the standard reference.ConclusionThe chemical structure of N-methyl-2-phenylpropan-1-amine is highly similar to methamphetamine, which is easy to cause interference for the detection of trace amounts of methamphetamine in wastewater using LC-TQ-MS. Therefore, in the actual analysis, the chromatographic retention time can be used to distinguish between N-methyl-2-phenylpropan-1-amine and methamphetamine.

Keywords

• forensic medicine
• toxicological analysis
• methamphetamine
• wastewater analysis
• mass spectrometry
• interfering substance
• n-methyl-2-phenylpropan-1-amine （phenpromethamine）