Determination of aspartame and phenylalanine in diet soft drinks by high-performance liquid chromatography with direct spectrofluorimetric detection

Application of spectrofluorimetric detection is proposed in this work for the determination of aspartame and its main hydrolysis product phenylalanine in diet soft drinks by high-performance liquid chromatography. Separation was achieved on a LiChrosorb RP18 column with the mobile phase methanol-acetonitrile-phosphate buffer (2:17:81), pH 4.3. Native fluorescence of the two analytes (lambda(ex) = 205 nm, lambda(em) = 284 nm) was used for detection. The detection limits for aspartame and phenylalanine were 0.06 mg 1(-1) and 0.01 mg 1(-1) and calibration graphs were rectilinear in the range 0.5-40 mg 1(-1) and 0.1-10 mg 1(-1), respectively. The proposed method was applied to determination of aspartame and phenylalanine in soft drinks (Diet Pepsi, Diet Coke and Diet Sprite) and the results obtained using two different detectors (spectrofluorimetric and spectrophotometric) were compared and discussed.