Functional group effects in laser-excited multi-photon photoionization of organics in liquid solutions

Of the organic compounds examined for possible two-photon photoionization behavior, 43% were found to yield analytically useful photoionization with excitation at 308 nm. Fifty-five per cent produced greater photoionization responses than aniline, the de facto photoionization standard. Additionally, 16 of the surveyed compounds were more photoionization efficient (i.e., exhibit higher photoionization per unit absorption cross-section) than aniline. It was found that photoionization is relatively easily achieved with primary amines, anilines and diamines. Less readily photoionized were primary and tertiary amides, esters, alkyl ethers, and most halogenated compounds, the main exceptions being the halogenated anilines. Tertiary amines and fluorinated compounds gave poor photoionization results.