Resonance enhanced two-photon ionization spectrometry of aromatic molecules in ambient pressure nitrogen gas

Various aromatic molecules have been detected simply and conveniently by measuring the photocurrent signal induced by resonance enhanced two-photon ionization. Volatile benzene derivatives were measured in the ppb~sub range by mixing the vapor of the analyte from a diffusion tube with nitrogen gas. Calibration curves were straight in the ppb~sub ppm range. Detection limits (S/N= 3) of eight benzene, derivatives were as low as ppb levels; the lowest detection limit was 0.8 ppb for aniline. The molecules with large molar absorptivities in isooctane gave the lower detection limits. Less volatile aromatic molecules were measured by the thermal vaporization technique; the solid sample was heated at a constant heating rate and the photocurrent signal was measured as a function of the temperature. Calibration curves were straight, and the lowest detection limit was 90 pg for triphenyl-amine. Some selective detections of mixtutes were possible within 10 min. This method may be useful for rapid identification and quantitation of organic adsorbates without any pretreatment.