Assessment of colloid formation and physical state distribution of trace polycyclic aromatic hydrocarbons in aqueous samples.

A tandem-cartridge system was established for studying colloid formation and physical state distribution of trace polycycic aromatic hydrocarbons (PAHs) in water. The effectiveness of the method for measuring the trace PAH colloids was demonstrated. With aqueous samples prepared by adding the PAH solutes with a small amount of organic solvent carrier, the potential of colloid formation increased with the hydrophobicity and concentration of the solute, but the incipient concentration for the colloid formation may be far lower than the aqueous solubility of the solute. After formation in water, the colloids showed remarkable stability at room temperature, and the stability was greatly reduced by elevated temperature and the presence of a small amount of inorganic electrolytes. The possible mechanism of destabilization of the colloids was discussed, and the mechanism might be of utility in providing insights into the physical state distribution of the solutes in various water samples. However, further effort to investigate the mechanism through fluorescence spectrophotometry was unsuccessful. The significance of the colloid formation in methods of preparation of aqueous samples and for measuring aqueous solubilities of PAHs and other hydrophobic compounds was illustrated. The results of this work demonstrate that it is undesirable to prepare aqueous solutions of PAHs or similarly hydrophobic compounds by vigorous mixing or the use of cosolvents, methods that are widely used in many studies for which aqueous solutions of such analytes are required.