Real-Time Multispecies Monitoring by Laser Mass Spectrometry

We propose to develop an ultrasentive detection system capable of measuring in real time multiple constituents in an gaseous sample. The key components of the detection system are: (1) a pulsed valve for injection of a gaseous sample in a vacuum chamber, (2) a single-photon ionization source at 118 nm (10.5 eV) generated by frequency tripling in a Xenon cell the 355 nm third-harmonic output of a Nd: YAG laser, and (3) a time-of-flight mass spectrometer (TOF/MS) for recording complete mass sprectra per laser pulse. A single-chamber design is described wherein ionization takes place near the orifice of the pulsed valve and the ions, after a short drift time, are accelerated into a 50-cm TOF drift tube. Under these conditions, detection levels of 1 part-per-trillion can be achieved on a timescale of seconds for typical aromatic molecules. The 10.5 eV ionization energy is sufficiently high to ionized nearly all nitrates, nitrosamines, amines, aromatics, holons, and most CFCs; yet it is of sufficiently low energy to avoid fragmentation of these molecules and to avoid ionization of common atmospheric constituents such as N2, O2, CO2, Co, Ar. It is especially well-suited to the detection of combustion byproducts of conventional waste munitions. The detection system is designed for mobility and routine operation and is projected to fit within the dimensions of 40x30x36in(L,W,H).