Two-Color Multiphoton Ionization with Ultraviolet and Visible Laser Excitation for the Determination of Polycyclic Aromatic Molecules in Solution

Characteristics of a two-color multiphoton ionization method with ultraviolet and visible pulsed laser excitation have been investigated for polycyclic aromatic molecules in nonpolar solvents. The photocurrent signal generated by the irradiation at 355 nm was enhanced by the additional action of the 532-nm light much more effectively than that at 1064 nm in terms of photon flux, except for a few molecules. The extent of the photocurrent enhancement depended on the solvent as well as on the laser pulse energy. The SN ratio was also affected by the laser pulse energy. Detection limits have been determined for selected molecules. The additional action of the 532-nm light certainly improved the detection sensitivity; the lowest detection limit (S/N= 3) for the two-color method was 9.4X10-12 M (1.7 pg ml-1) for anthracene.