MEASUREMENT OF HINOKITIOL BY HPLC 525 CONCLUSION We present a simple HPLC method with dual-wavelength UV detection for determina- tion of hinokitiol, using an RP-4 column. The sensitivity of our method was moderate, but was suffi cient for the measurement of hinokitiol levels in the tested personal care products. REFERENCES (1) J. Nault, A capillary gas chromatographic method for thujaplicins in western red cedar extractives, Wood Sci. Technol., 21, 311–316 (1987). (2) Y. Inamori, S. Shinohara, H. Tsujibo, T. Okabe, Y. Morita, Y. Sakagami, Y. Kumeda, and N. Ishida, Antimicrobial activity and metalloprotease inhibition of hinokitiol-related compounds, the constitu- ents of Thujopsis dolabrata S. and Z. hondai MAK, Biol. Pharm. Bull., 22, 990–993 (1999). (3) Y. Inamori, Y. Sakagami, Y. Morita, M. Shibata, M. Sugiura, Y. Kumeda, T. Okabe, H. Tsujibo, and N. Ishida, Antifungal activity of hinokitiol-related compounds on wood-rotting fungi and their insecti- cidal activities, Biol. Pharm. Bull., 23, 995–997 (2000). (4) E. L. Johnson and A. J. Cserjesi, Gas-liquid chromatography of some tropolone-TMS ethers, J. Chro- matogr., 107, 388 (1975). (5) F. Hanafusa, K. Nakamura, S. Togano, and T. Ohta, Determination of hinokitiol in cosmetic products by HPLC, Bunseki Kagaku, 38, 124–128 (1989). (6) M. Endo, T. Mizutani, M. Matsumura, M. Moriyasu, M. Ichimaru, A. Kato, and Y. Hashimoto, High- performance liquid chromatographic determination of hinokitiol in cosmetics by the formation of di- fl uoroborane compounds, J. Chromatogr., 455, 430–433 (1988). (7) L. Dyrskov, B. W. Strobel, B. Svensmark, and H. C. B. Hansen, Beta-thujaplicin: New quantitative CZE method and adsorption to goethite, J. Agric. Food. Chem., 52, 1452–1457 (2004).