Adsorpition of tryptophan onto calcum carbonate surface.

Adsorption of tryptophan onto CaCO3 at constant ionic strength (0.05 M Nacl) and from dilute aqueous solution (10(-4) M to 10(-3) M tryptophan) is reported. Adsorption was primarily determined by the charge characteristics of both the adsorbate amino acid and adsorbent CaCO3. When both adsorbate and adsorbent are semicharged, tryptophan ions are expelled away from the CaCO3-solution interface. Tryptophan is only removed by CaCO3 in a narrow pH range, 6.0 greater than pH less than 8.5 within which CaCO3 has positive charges, and tryptophan is negatively charged. The pH of zero point of charge, pHzpc, of CaCO3 was also determined by alkalimetric tritration and coagulation techniques and a value of 9.50 +/- 0.5 was found. These preliminary finding demonstrate primarily that interfacial chemical reactions play an important role in the temporal and spatial transformation of dissolved organic matter in natural water systems.