Analytical Sciences

Real-time Monitoring of Monochlorinated Benzene and Polychlorinated Biphenyls in the Gas Phase with On-line Detection: High Chemical Selectivity of Resonance-Enhanced Two-Photon Ionization

Shinsaku DOBASHI,*¹ Masaharu KIRA,*² Ryuichiro TANAKA,*³ Yoshinori IZAWA,*³ Akihide WADA,*⁴ and Michikazu HARA*⁴

*1 Nagasaki R&D Center, Mitsubishi Heavy Industries Ltd., 5-717-1 Fukahori-machi, Nagasaki 851-0392, Japan
*2 Machinery Headquarters, Mitsubishi Heavy Industries Ltd., 16-5 Konan 2-chome, Minato-ku, Tokyo 108-8215, Japan
*3 Nagasaki Shipyard & Machinery Works, Mitsubishi Heavy Industries Ltd., 1-1 Akunoura-machi, Nagasaki 850-8610, Japan
*4 Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 184-8584, Japan

The development of molecular spectroscopy has enabled us to select chlorinated aromatic hydrocarbons very rapidly. In particular, the laser ionization TOFMS (time-of-flight mass spectrometry) method is expected to be useful as an on-line, selective, and sensitive method. In the present work, real-time laser ionization TOFMS measurements were carried out on gaseous chlorinated aromatic hydrocarbons. The laser ionization method used resonance-enhanced two-photon ionization with the direct introduction of gas into the vacuum chamber. This method for analyzing aromatic hydrocarbons was developed using a pulsed supersonic molecular beam method. In the context of developing a highly selective and sensitive method, excitation of monochlorinated benzene at λ = 263.07 nm was found to be effective in the wavelength region from 263 nm to 265 nm. Also the excitation of polychlorinated biphenyls at λ = 266 nm was found to be substantially more effective than at λ = 280, 300 or 320 nm. The achievable sensitivity for real-time (1 min) measurements using the laser ionization TOFMS technique was found to be in the ppbV range.

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