Determination of kojic acid in a skin-whitening cosmetic by high-performance liquid chromatography coupled with ultraviolet detection after pre-column derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole.

Various methods for the determination of kojic acid (KA), a skin-whitening agent, have been reported by high-performance liquid chromatography (HPLC). In this study, the concentration of KA in a skin-whitening cosmetic was analyzed by HPLC with ultraviolet detection (380 nm) after pre-column derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) in order to improve the sensitivity. The HPLC column was 150 mm x 3.0 mm i.d., containing 5 microm particles of C18 packing material. The mobile phase was prepared by the addition of acetonitrile (550 ml) to 450 ml of Milli-Q water containing trifluoroacetic acid (0.1 v/v%). The samples were eluted from the column at room temperature at a flow rate of 0.35 ml/min. The retention time of NBD-KA was 7.8 min. A standard curve was obtained after derivatization with NBD-F in borate buffer (pH 9.0) at 40 degrees C for 7 min. The calibration plot was linear, in the range of 0.25-5 microg/ml with an r2 value of 0.9982, and the lower limit of detection was 0.06 microg/ml (at a signal-to-noise ratio of 3:1; absolute amount of 0.4 ng/20 microl injection). The coefficient of variation was less than 9.6%. It was found that the amount of KA in a skin-whitening cosmetic was 237 +/- 14 microg/ml (range: 219-255 microg/ml). Recovery in addition-recovery tests was within the range of 83.4% to 98.1%.