HIGHLY SENSITIVE DETERMINATION OF AROMATIC-MOLECULES ON THE WATER-SURFACE BY LASER 2-PHOTON IONIZATION AT 355 NM

The laser two-photon ionization technique has been applied to several aromatic molecules on the surface of water in ambient air. The third harmonic of a NdYAG laser (355 nm) was used for excitation and ionization. The photoionization charge (the area of the signal) was linearly proportional to the solute concentration when the incident angle of the laser beam was 85-degrees. Less soluble molecules exhibited larger signals when the molar absorptivities were equal. The detection limits of aminoanthracene and methylanthracene were 0.2 mug/dm3 (ppb). They are almost identical to those obtained at 337 nm, but slightly inferior to those obtained in hexane solution.