6 JOURNAL OF COSMETIC SCIENCE diol, (D) 2-N-eicosanoylamino-octadecane-1,3-diol, (E) 2-N-docosanoylamino­ octadecane-1,3-diol, and (F) 2-N-tetracosanoylamino-octadecane-1,3-diol. DETERMINATION OF THE HAIR LIPIDS BY CHROMATOGRAPHY The optimal conditions for extraction of hair lipids, excluding contaminated lipids, were examined for the relationship between hexane incubation time after twice shampooing hair fibers and the extracted lipid contents. When the square root of time was plotted against the relative extracted lipid content, a linear plotting was obtained during 5 to 30 min of incubation with hexane (Figure 2). In general, the following equation is used for the diffusion of a solute into a cylindrical fiber of infinite length (26): C/C00 = 4(Dt/(Tir2))112 where C/C00 represents relative solute uptake at a certain time (t), D is the diffusion coefficient, and r is the radius of the cylindrical fiber. According to this equation, if diffusion of the solute occurs, the relative solute uptake plotted against the square root of time should become linear because of the constant D, 'IT, and r. The observed linear line (Figure 2) implies the existence of diffusion of the lipids from the hair inside to the outside during the incubation. Therefore, in our study, a 5-min incubation with hexane was performed prior to the extraction of hair lipids to delete contaminated lipids. 0.4 0.0 0 30 min 5 min 10 min 20 min t f 2min t t . ............ ···· .... + ··········· 1 min + 1 2 3 4 5 Root square of hexane incubation time 6 min112 Figure 2. Effect of hexane incubation time after twice shampooing of hair fibers on extracted lipid contents. Each point represents the mean ± SD calculated in five hair samples for each hexane incubation time. Relative extracted lipid content was defined as a ratio of lipid contents extracted at a certain time (t) to that of total lipids exhaustively extracted.

HAIR LIPID COMPOSITION 7 HCs, SQ, WEs, TGs, and FAs in the extractable lipids were determined by HPTLC­ densitometry according to the conventional method (16, 1 7). A representative chromato­ gram is shown in Figure 3. MEA in the integral lipids was determined by HPLC following its derivatization with ADAM according to a previously reported method (6), and a representative chromatogram is shown in Figure 4. CH in the lipids was deter­ mined by GC, based on a previously reported method (7), and a representative chro­ matogram is depicted in Figure S. Sphingoids generated by hydrolysis of CE Rs in the lipids were determined by HPLC following their derivatization with OP A (Figure 6). The major and minor sphingoids were identified as erythro (C 18 -)dihydrosphingosine (peak C in Figure 6), and (C 18 -)sphingosine (peak A in Figure 6) by comparison with authentic standards. Peak D in Figure 6 was identified as erythro-C 20 -dihydro­ sphingosine based upon comparison with GC/MS data for acetylated and silylated sphin- 12 cm...-----------....----. HCs 9cm I SQ WEs I TGs 6cm I FAs 3cm 0cm A B C D E F Figure 3. A HPTLC chromatogram of lipid references and extractable lipids. Lane A: tetracosane. Lane B: squalene. Lane C: cetyl palmitate. Lane D: tripalmitin. Lane E: palmitic acid. Lane F: extractable lipids.