Vv. Gridin et al., DETERMINATION OF AQUEOUS SOLUBILITY AND SURFACE-ADSORPTION OF POLYCYCLIC AROMATIC-HYDROCARBONS BY LASER MULTIPHOTON IONIZATION, Analytical chemistry (Washington), 70(13), 1998, pp. 2685-2692
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.