HPLC DETERMINATION OF KOJIC ACID 211 Table III Level of KA in a Skin-Whitening Cosmetic and Recovery of Spiked KA Assay Content (μg/ml) Recovery (%) Added (30.0 μg) Added (50.0 μg) Day 1 244 84.2 96.8 Day 2 239 88.6 98.1 Day 3 228 89.6 91.3 Day 4 255 91.7 92.2 Day 5 219 83.4 85.9 Avg. ± S.D. (C.V.) 237 ± 14 (5.9%, n = 5) 90.2 ± 4.9% (5.4%, n=10) CONCLUSION We have developed an HPLC–UV method for the determination of KA in a skin-whitening cosmetic by using NBD-F as a labeling reagent. A tested skin-whitening cosmetic was found to contain KA at a mean concentration of 237 μg/ml using the present system. This method is simple and convenient, and should be suitable for routine quality assess- ment of skin-whitening cosmetics. REFERENCES (1) K. Kimura, M. Hirokado, K. Yasuda, and M. Nishijima, Determination of kojic acid in various com- mercial foods by HPLC, J. Food Hyg. Soc. Jpn., 41, 70–73 (2000). (2) S. C. Huang, C. C. Lin, M. C. Huang, and K. C. Wen, Simultaneous determination of magnesium ascorbyl phosphate, ascorbyl glucoside, kojic acid, arbutin and hydroquinone in skin whitening cosmet- ics by HPLC, J. Food Drug Anal., 12, 13–18 (2004). (3) C. H. Lin, H. L. Wu, and Y. L. Huang, Combining high-performance liquid chromatography with on- line microdialysis sampling for the simultaneous determination of ascorbyl glucoside, kojic acid, and niacinamide in bleaching cosmetics, Anal. Chim. Acta, 581, 102–107 (2007). (4) Y. Shih, Simultaneous determination of magnesium L-ascorbyl-2-phosphate and kojic acid in cosmetic bleaching products by using a microbore column and ion-pair liquid chromatography, J. AOAC Int., 84, 1045–1049 (2001). (5) Y. Shih and J. M. Zen, Voltammetric determination of kojic acid in cosmetic bleaching products using a disposable screen-printed carbon electrode, Electroanalysis, 11, 229–233 (1999). (6) X. F. Yang and H. J. Zhang, Sensitive determination of kojic acid in foodstuffs using PVP (polyvinylpyrrolidone) modifi ed acetylene black paste electrode, Food Chem., 102, 1223–1227 (2007). (7) J. Liu, D. Zhou, X. Liu, K. Wu, and C. Wan, Determination of kojic acid based on the interface en- hancement effects of carbon nanotube/alizarin red S modifi ed electrode, Colloids Surf. B, 70, 20–24 (2009). (8) K. Imai, Analytical chemical studies on high-performance recognition and detection of bio-molecules in life, Yakugaku Zasshi, 123, 901–917 (2003). (9) Y. Higashi, S. Nakamura, H. Matsumura, and Y. Fujii, Simultaneous liquid chromatographic assay of amantadine and its four related compounds in phosphate-buffered saline using 4-fl uoro-7-nitro-2,1,3- benzoxadiazole as a fl uorescent derivatization reagent, Biomed. Chromatogr., 20, 423–428 (2006). (10) Y. Higashi, M. Sakata, and Y. Fujii, Simultaneous determination of the N-dealkylated metabolites of four butyrophenone-type agents in rat plasma by HPLC with fl uorescence detection after precolumn derivatization with 4-fl uoro-7-nitro-2,1,3-benzoxadiazole, J. Liq. Chromatogr. Rel. Technol, 30, 2747– 2754 (2007). (11) T. Fukushima, J. Kawai, K. Imai, and T. Toyo’oka, Simultaneous determination of D- and L-serine in rat brain microdialysis sample using a column-switching HPLC with fl uorimetric detection, Biomed. Chromatogr., 18, 813–819 (2004).

JOURNAL OF COSMETIC SCIENCE 212 (12) Y. Higashi, R. Gao, and Y. Fujii, Determination of fl uoxetine and norfl uoxetine in human serum and urine by HPLC using a Cholester column with fl uorescence detection, J. Liq. Chromatogr. Rel. Technol., 32, 1141–1151 (2009). (13) T. Toyo’oka, T. Mantani, and M. Kato, Characterization of labelling and de-labelling reagents for detec- tion and recovery of tyrosine residue in peptide, Biomed. Chromatogr., 17, 133–142 (2003). (14) Y. Higashi and Y. Fujii, HPLC-UV analysis of phenol and chlorophenols in water after pre-column de- rivatization with 4-fl uoro-7-nitro-2,1,3-benzoxadiazole, J. Liq. Chromatogr. Rel. Technol., 32, 2372– 2383 (2009). (15) Y. Higashi and Y. Fujii, HPLC-UV analysis of eugenol in clove and cinnamon oils after pre-column derivatization with 4-fl uoro-7-nitro-2,1,3-benzoxadiazole, J. Liq. Chromatogr. Rel. Technol., 34, 18–25 (2011).