Mitsubishi Heavy Industries, Ltd. (MHI) has further improved its original high-speed analysis technology developed by combining vacuum ultraviolet light ionization, ion trapping, and time-of-flight type mass spectrometry with the aim of monitoring trace-level toxic substance in exhaust gas from incinerator furnaces in an attempt to increase the analytical sensitivity and extend the applicability of the technology to actual plants. As a result, the technology has made it possible to analyze trichlorobenzene (T3CB), a dioxin precursor, in a gaseous state in twenty seconds with a sensitivity of 80 ng/m³N, and pentachloro-dibenzofuran (P5CDF), a type of dioxin, in a solvent in sixteen minutes with a sensitivity of 1 pg using the selective accumulation of target substances and separation of interfering substances in the ion trap. These results show that higher speed and higher sensitivity in analyzing toxic substances than had been previously possible can be achieved and the adverse effects of impurities contained in actual gas reduced. In addition, MHI has developed a cleaning procedure for the vacuum ultraviolet light irradiating window to contribute to extending the service life of the analyzing system.