Field-portable gas chromatography with transmission quadrupole and cylindrical ion trap mass spectrometric detection: Chromatographic retention index data and ion/molecule interactions for chemical warfare agent identification

Field-portable gas chromatography–mass spectrometry (GC–MS) is well-suited for the reliable identification of dangerous chemicals. The chemical warfare agent (CWA) O-ethyl-S-2-diisopropylaminoethyl methylphosphonothiolate (VX) and many VX degradation products are challenging GC–MS analytes for a transmission quadrupole detector, as resulting 70 eV electron ionization mass spectra contain little high mass information. Approaches were explored to detect these analytes using two field-portable GC–MS systems having either a transmission quadrupole or a cylindrical ion trap (CIT) detector. Spectral matching alone for the transmission instrument did not unambiguously identify VX and several related analytes, while use of mass spectra and retention index information resulted in accurate identification. Ion/neutral interactions in the CIT produced pseudomolecular ions ([M+H]+) for VX-related compounds and also for other CWA nerve agent compounds. In addition to [M+H]+, protonated dimers ([2M+H]+) were produced in the CIT for phosphonofluoridate compounds such as sarin. The CIT ion/molecule reactions were concentration-dependent, and mass assignment shifts were not unusual with increasing analyte concentrations. For these reasons the CIT detector is potentially problematic for reliable chemical identification by technician-level users under non-laboratory conditions.

Two field-portable GC–MS systems were used for chemical warfare agent detection. With GC retention index information, electron ionization and a quadrupole mass filter identified analytes such as VX which normally require chemical ionization. Self-CI in a cylindrical ion trap detector produced pseudomolecular ions such as the protonated dimer of sarin (GB) shown below, although concentration-dependent mass spectra were seen, as well as mass axis shifts due to space charge.Figure optionsDownload high-quality image (113 K)Download as PowerPoint slide