JOURNAL OF COSMETIC SCIENCE 386 mean, and recoveries were within the range of 92.0% to 102.8%. In the interday assay, the range of standard deviation was within 5.4% to 9.4% of the mean, and recoveries were within the range of 90.5% to 101.0%. INTERFERENCE Skin lotion usually contains paraben, ester possessing phenol-like hydroxyl group, as an effective preservative. Therefore, selectivity was preliminarily investigated on the detec- tion of NBD-hinokitiol peak. All retention times of methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, isopropyl 4-hydroxybenzoate, butyl 4-hydroxybenzoate, isobutyl 4-hydroxybenzoate, and benzyl 4-hydroxybenzoate deriva- tives (each paraben concentration 1 μg/ml) by NBD-F were 6.9 min. Peaks of tested paraben derivatives were found to be slightly separated from NBD-hinokitiol peak (re- tention time 7.2 min). One question arises about same retention time of paraben deriva- tives. Although it is considered that these parabens will be hydrolyzed to generate Table I Sensitivity of Various Methods for Determination of Hinokitiol Method Limit of detection Reference Capillary GC Not described 1 GC Not described 4 HPLC 40 pg 6 Capillary zone electrophoresis 0.21 μM 7 HPLC 1 ng (at 240 nm), 2 ng (at 345 nm) 8 HPLC 0.33 ng 0.05 μg/ml This article Table II Intra- and Interday Assay Reproducibility for Determination of Hinokitiol Hinokitiol (μg/ml) Measured (μg/ml, mean ± S.D., n = 5) C.V. (%) Recovery (%) Intraday assay 0.2 0.184 ± 0.013 7.1 92 1 0.942 ± 0.058 6.2 94.2 4 4.11 ± 0.19 4.6 102.8 Interday assay 0.2 0.181 ± 0.017 9.4 90.5 1 0.962 ± 0.081 8.4 96.2 4 4.04 ± 0.22 5.4 101 C.V.: Coeffi cient of variation.

HPLC DETERMINATION OF HINOKITIOL 387 Figure 5. Typical chromatogram of a skin lotion sample (500 μl/100 ml, 200-fold diluted) after derivatiza- tion with NBD-F. The sample was reacted with NBD-F for 10 min in borate buffer, pH 9.0, at 60°C. Reten- tion time of NBD-hinokitiol: 7.2 min (arrowed peak). 4-hydroxybenzoate under derivatization (60°C, pH 9.0, 10 min), further studies are needed to solute the point. APPLICATION TO SKIN LOTION Figure 5 shows a typical chromatogram obtained from a skin lotion sample. The peak of NBD-hinokitiol was detected at 7.2 min, and the concentration of hinokitiol in the cos- metic was determined as follows. The described method was used to determine hinokitiol in the skin lotion and in samples spiked with standards. As shown in Table III, the concentration of hinokitiol in the skin