IMMOBILIZATION OF AQUEOUS PYRENE BY DISSOLVED HUMIC-ACID

Pyrene is frequently used as a fluorescent probe in the study of solut ion environments. Purging with nitrogen is a common practice for the e limination of oxygen from solutions, but this procedure leads to the l oss of pyrene through carry-over in the nitrogen stream. The presence of humic acid in solution, even in small quantities, can have a signif icant retarding effect on this evaporation of pyrene. Based on the det ergent model of humic acid, this is ascribed to its ability to sequest er pyrene in pseudomicellar structures; This immobilization of pyrene has been found to depend on the molecular size and flexibility of the humic acid in question. The presence of metal ions in solution also ex erts a strong influence by enhancing the detergent character of the hu mic acid. The degree of pyrene immobilization by dissolved humic acid can be used as a measure of its association with hydrophobic species. (C) 1997 Elsevier Science B.V.