DETERMINATION OF AQUEOUS SOLUBILITY AND SURFACE-ADSORPTION OF POLYCYCLIC AROMATIC-HYDROCARBONS BY LASER MULTIPHOTON IONIZATION

Polycyclic aromatic hydrocarbons (PAHs) are of considerable analytical interest due to their environmental effects. On-line monitoring of th ese compounds based on microdroplet sampling requires accurate charact erization of their solubilities and surface adsorption. A new method t o determine aqueous solubility and surface adsorption of PAHs is sugge sted, using a combination of microdroplet sampling and multiphoton ion ization-based fast-conductivity (MPI-FC) techniques. Controlled drople t contamination by PAHs was performed by external deposition upon dire ct contact with renewable water droplets (congruent to 10 mu L). Our a pproach relies on the finding that, at the onset of aqueous equilibriu m solubility, X-E, a sharp increase in the detected photocharges is re corded. We show that this is directly related to enhanced surface adso rption of a particular PAH material. This behavior manifests itself in slope variation of the respective calibration curves, The PAH materia ls used, which have provided about four decades variation in X-E figur es, were anthracene, perylene, pyrene, and phenanthrene. Applicability of the method for studying the surface excess and adsorption is speci fied. The MPI-FC technique provides an easy analytical tool for measur ing low aqueous solubility of organic compounds and characterization o f their adsorption, with no need for laborious sample preparation rout ines.