|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1991 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1990 : ¥1,400,000 (Direct Cost : ¥1,400,000)
A highly sensitive photoionization detection system with multi-wavelength excitation was constructed, by the additional equipment of a current amplifier, a recorder, a preamplifier, and optical parts, to the present instrument ; it has the resolution time of the order of nanoseconds and has the current detection sensitivity of subpicoampere levels. This system also has fluorescence detection function.
Photocurrent signals induced by the action of ultraviolet (UV) light alone, and the cooperative action of UV and visible (VS) or UV and infrared (IR) light were compared for about twenty kinds of polycyclic aromatic molecules in solution. The additional action of the IR light enhanced the photocurrent signal generated by UV light irradiation. On the other hand, the photocurrent decrease was observed for a few molecules, when the VS light acted additionally ; though most of molecules showed photocurrent increase as in the case of the IR light. Photolonization mechanisms were investigated for anth6racene, perylene, and benzo[alpyrene. It is suggested that the IR light acts through the geminate cation-electron pair, while the VS light acts mainly through the first excited singlet (and/or triplet) state induced by one-photon absorption of the UV light.
Signal-to-noise ratios were investigated at several laser irradiation conditions. By optimizing experimental conditions, detection limits of some molecules were determined ; the lowest detection limit was 1.7 pg/ml for anthracene by the simultaneous action of the UV and the VS light. The VS light was more effective than the IR light for improving the detection sensitivity, if the comparison is made in terms of the identical photon density.
In order to extend the present method, a photoionization'cell with submicroliter volume, and a fiber-optic detection cell, have been constructed ; further studies are now in progress.