of HS is their ability to interact with metal ions (3). More-The adsorption of several fractions of humic and fulvic acids on over, the functional groups responsible for the affinity of HS silver colloids was studied by means of surface-enhanced Raman for metallic ions are also involved in the strong interaction spectroscopy. The short-range mechanism of this technique was observed between these organic macromolecules and minapplied in the determination of the chemical groups which are eral surfaces occurring in soils, sediments and water (4-7).
directly attached to the metallic surface. Adsorption of humic
In fact, the adsorption of HS on inorganic surfaces is a substances was found to be very sensitive to pH, to the electric process of a very high importance in nature, and which has charge of both the humic substances and the metallic surface, and been scarcely studied up to now. The study of the adsorption to the size of the adsorbed macromolecules. From the obtained of macromolecules on colloidal particles is an interesting results, a model for the adsortion mechanism of these macromolecules is proposed on the basis of a conformational change and a topic which has deserved much attention by several authors variation of their electric charge on modifying the pH. FTIR spec- (8,9), although experimental work must be done, in order tra of some of the extracted fractions and SERS spectra of o-, to elucidate the mechanism of their adsorption on colloids.
m-, and p-hydroxybenzoic acids, used as molecular models for
Infrared and nuclear magnetic resonance spectroscopies humic substances, were also obtained in order to better attribute are two techniques which have been largely employed in the the SERS spectra of these humic substances. ᭧ 1998 Academic Press structural characterization of HS (10,11). Raman spectros-Key Words: SERS; humic substances; silver colloids; adsorption. copy is a powerful technique, which can be used in the study of complex macro-molecules in acqueous solution, owing to the weak Raman signal of water. However, Raman spectros-