POSTCOLUMN EXCITATION OF AFLATOXINS USING CYCLODEXTRINS IN LIQUID-CHROMATOGRAPHY FOR FOOD ANALYSIS

Measurement of fluorescence increase was used for the comparative quan tification of the effect that several cyclodextrins (alpha-, beta-, he ptakis-2,6-beta-o-dimethyl- and gamma-) produce on the fluorescent res ponse of aflatoxins B-1 and G(1). This constitutes a new chromatograph ic method with stability of the mobile phase, and shows general improv ements in the chromatographic conditions with respect to other methods (especially those using an iodine reservoir as a postcolumn reactor). A C-18-type column was used, with methanol-water (60:40, v/v) as the mobile phase. The excitation phase of the natural fluorescence of afla toxins, a 10(-2) M solution of each cyclodextrin, was introduced postc olumn. The determination of the elution order aflatoxin G(2) > G(1) > B-2 > B-1 was performed for each phase in less than 15 min. As expecte d using an aqueous-alcoholic medium, an increase in the fluorescence r esponse of aflatoxins with an unsaturated furanic ring was found to oc cur with all the cyclodextrins studied, except gamma-cyclodextrin. The observed increase was larger for heptakis-2,6-beta-o-dimethyl- than f or beta-cyclodextrin (to our knowledge, the only cyclodextrin previous ly described in the literature to serve for the determination of aflat oxins). The difference is of the order of 70.1-fold in the case of afl atoxin G(1) and 45.2-fold in the case of aflatoxin B-1. The detection limit in the mobile phase used was determined (for aflatoxin B-1) for beta-cyclodextrin and 2,6-beta-o-dimethylcyclodextrin (signal-to-noise ratio 1:3) to be 4 and 9 mg l(-1), respectively.