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

A derivatization reaction for resin acids (RAs), commonly found in untreate d pulp mill effluents, was performed and evaluated in the separation and se nsitive detection of the resin acids by cyclodextrin-modified capillary ele ctrophoresis. The procedure involved the reaction of 4-bromomethyl-7-methox ycoumarin, a fluorescent label, with the carboxyl group of the resin acid i n the presence of potassium carbonate to form an ester. Both MS data and HP LC analysis equipped with UV or scanning fluorescence revealed that the der ivatization was free from side products and very quantitative. The derivati zed esters were very stable and fluoresced optimally at 325 nm, excitation and 400 nm emission, an ideal condition for capillary electrophoresis equip ped 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 separati on and detection of the derivatized RAs. Separation at pH 4.5 and +15 kV ap plied potential using 42.5 mM sulfobutylether-beta-CD and 12.5 mM methyl-be ta-CD in 50 mM sodium acetate has allowed the achievement of baseline separ ation of eight very closely related derivatized resin acids. With laser-ind uced fluorescence, the extrapolated concentration limit of detection (3 sig ma) of the resin acid esters was about 10-20 mu g/l, based on capillary ele ctrophoresis analysis of a standard solution containing 500 mu g/l of each derivative. (C) 1999 Elsevier Science B.V. All rights reserved.