Combining high-performance liquid chromatography with on-line microdialysis sampling for the simultaneous determination of ascorbyl glucoside, kojic acid, and niacinamide in bleaching cosmetics.

We have used on-line microdialysis sampling coupled with high-performance liquid chromatography and UV-vis detection to simultaneously determine the contents of ascorbyl glucoside (AA-2G), kojic acid (KA), and niacinamide (VitB(3)) in commercial bleaching cosmetics. Our results indicate that AA-2G, KA, and VitB(3) separated well within 4.5 min on a reverse-phase Hypersil Fluophase PFP column when eluting with 0.020 M phosphate buffer solution in 40% (v/v) methanol at pH 5.5. The calibration curves were linear over the ranges 0.068-304, 0.071-284, and 0.024-488 microg mL(-1) for AA-2G, KA, and VitB(3), respectively, with correlation coefficients for the linear regression analyses falling within the range 0.9982-0.9999. The detection limits for AA-2G, KA, and VitB(3) were 0.01, 0.01, and 0.007 microg mL(-1), respectively. The detection wavelength was robust when the levels of the analytes in the samples were high (0.1-2%). The analytes were all detected using ultraviolet light (254 nm). The compounds diffuse through the membrane more readily when KA and VitB(3) are in their molecular forms and AA-2G is ionized. The recoveries were in the range 92-106% with good reproducibility (R.S.D.=3.9-8.7%). We used this procedure to assay six commercially available bleaching cosmetics; our results confirmed not only the precision of the method but also the claims made on the labels of the cosmetics. This approach provides a very simple means to determine the contents of AA-2G, KA, and VitB(3) in various dosages in bleaching cosmetics.