Multipass laser mass spectrometer with extreme jet-cooled pulsed gas

Abstract

We have developed a photon accumulated laser mass spectrometer that enables us to identify isomers of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran. This system is comprised of a high temperature (230°C) pulsed gas injector (PGI), multimirror multipath system (MMS), and the conventional time-of-flight mass spectrometer. The PGI induces the formation of a choked supersonic jet gas pulse that cools down to a temperature to restrain fragmentation and reduces vibrational and rotational thermal noises. The results suggest that the excited lifetime numbers and fragment dynamics of these species change completely with jet cooling of molecules. The MMS enhances the soft ionization efficiency (by a factor of 1000 over a single path system) through photon accumulation by extending the irradiation duration (to about 40ns) and volume, and it further minimizes fragmentation by carefully controlling the laser intensity distribution within the ionization volume. For the typical isomer 2,3,4,7,8-pentachlorodibenzofuran, the system achieved a detection threshold (S/N ratio=3) of 410ppq (equivalent to 4.4ng∕Nm3).