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J. Cosmet. Sci., 64, 381–389 (September/October 2013) 381 Determination of hinokitiol in skin lotion by high-performance liquid chromatography–ultraviolet detection after precolumn derivatization with 4-fl uoro-7-nitro-2,1,3-benzoxadiazole YASUHIKO HIGASHI and YOUICHI FUJII, Department of Analytical Chemistry, Faculty of Pharmaceutical Sciences, Hokuriku University, Kanazawa 920-1181, Japan. Accepted for publication February 28, 2013 Synopsis Hinokitiol, a potent, broad-spectrum antibacterial agent, is a component of various personal care products. In this study, the concentration of hinokitiol in skin lotion was analyzed by means of high-performance liquid chromatography–ultraviolet detection (380 nm) after precolumn derivatization with 4-fl uoro-7-nitro-2,1, 3-benzoxadiazole (NBD-F). A standard curve was obtained after derivatization of the authentic compound with NBD-F in borate buffer (pH 9.0) at 60°C for 10 min. The retention time of NBD-hinokitiol was 7.2 min. The calibration plot was linear in the range of 0.2 to 4 mg/ml with an r2 value of 0.9985, and the lower limit of detection was 0.05 μg/ml (at a signal-to-noise ratio of 3, absolute amount of 0.33 ng/20 μl injection). The coeffi cient of variation was less than 9.4%. It was found that the amount of hinokitiol in the tested skin lotion was 194 ± 14 μg/ml (range: 180–212 μg/ml). Recovery in addition-recovery tests was within the range of 84.5% to 98.0%. This system is simple, sensitive, and convenient, and should be suitable for routine quality assessment of personal care products containing hinokitiol. INTRODUCTION Hinokitiol (β-thujaplicin, 4-isopropyl-2-hydroxycyclohepta-2,4,6-trien-1-one Fig. 1) is a naturally occurring toxic compound belonging to the class of tropolones that contain an unsaturated seven-membered carbon ring. The compound is found in heartwood of several cupressaceous plants, such as western red cedar (Thuja plicata), eastern white cedar (T. occidentalis), hinoki cypress (Chamaecyparis obtusa), and hiba (Thujopsis dolabrata) (1,2). Since hinokitiol has potent antibacterial activity (minimum inhibitory concentration of 0.2 μg/ml for Staphylococcus epidermidis and Daedalea dickinsii) (2,3), it is often added to skin lotions, body soaps, and other personal care products. Direct determination of hinokitiol, by means of gas chromatography (GC) or high- performance liquid chromatography (HPLC) is diffi cult because of the chelating activity Address all correspondence to Yasuhiko Higashi at y-higashi@hokuriku-u.ac.jp.