Abstract
In aromatic hydrocarbons there are many organic hazards such as polychlorinated biphenyls and chlorinated benzenes. Emissions of such chemicals from environmental protection equipments and other facilities have become a major social issue, and evaluation of toxicity concentration requires methods having both high precision and high chemical selectivity. Recently, development of molecular spectroscopy has enabled us to select aromatic hydrocarbons very rapidly. In particular, the laser ionization TOFMS (Time of Flight Mass Spectrometry) method is expected to be a powerful for on-line, selective and sensitive method. In this report, real-time laser ionization TOFMS measurements were carried out on gaseous aromatic hydrocarbons. The laser ionization method was used resonance enhanced multi-photon ionization (REMPI) with direct introduction of gas into the vacuum chamber. This method for analyzing aromatic hydrocarbons was developed using a pulsed supersonic molecular beam technique. Excitation of monochlorinated benzene at λ = 263.07 nm was found to be effective in the wavelength from 263 nm to 265 nm. Excitation of polychlorinated biphenyls at λ = 266 nm was found to be substantially more effective than at λ=280, 300 or 320 nm. Also, picosecond excitation for polychlorinated biphenyls underwent more efficient ionization (by a factor of over 10) and less fragmentation than nanosecond excitation. The achievable sensitivity for real-time (1 minute) measurement using the laser ionization TOFMS technique was found to be in the pptV range Accordingly, the laser ionization TOFMS technique implies a useful method for the on-line monitoring of aromatic hydrocarbons. In the future we will pursue practical application in the form of a safety management-monitoring device for aromatic hydrocarbons.
