Derivatization of resin acids with a fluorescent label for cyclodextrin-modified electrophoretic separation

A derivatization reaction for resin acids (RAs), commonly found in untreated pulp mill effluents, was performed and evaluated in the separation and sensitive detection of the resin acids by cyclodextrin-modified capillary electrophoresis. The procedure involved the reaction of 4-bromomethyl-7-methoxycoumarin, a fluorescent label, with the carboxyl group of the resin acid in the presence of potassium carbonate to form an ester. Both MS data and HPLC analysis equipped with UV or scanning fluorescence revealed that the derivatization was free from side products and very quantitative. The derivatized esters were very stable and fluoresced optimally at 325 nm, excitation and 400 nm emission, an ideal condition for capillary electrophoresis equipped with He-Cd laser-induced fluorescence. Cyclodextrin-modified capillary electrophoresis using a mixture of negatively charged sulfobutylether-beta-CD (SBCD) and neutral methyl-beta-CD (MECD) was then optimized for separation and detection of the derivatized RAs. Separation at pH 4.5 and +15 kV applied potential using 42.5 mM sulfobutylether-beta-CD and 12.5 mM methyl-beta-CD in 50 mM sodium acetate has allowed the achievement of baseline separation of eight very closely related derivatized resin acids. With laser-induced fluorescence, the extrapolated concentration limit of detection (3 sigma) of the resin acid esters was about 10-20 mu g/l, based on capillary electrophoresis analysis of a standard solution containing 500 mu g/l of each derivative. (C) 1999 Elsevier Science B.V. All rights reserved.