4 JOURNAL OF COSMETIC SCIENCE reference. The standard curve of elution volume and molecular weight was established. The weight-average molecular weights of the samples were calculated from the standard curve with the Chem-Lab software. Degree ofdeacetylation determination. The degree of deacetylation of prepared water-soluble chitosans from the ultrasonic method was determined by FTIR methods (37). Chitosan powder was mixed with KBr (1:100) and pressed into a pellet. The absorbances of amide 1 (1655 cm -•) and the hydroxyl band (3450 cm -•) were measured using a Bio-Rad FTS- 155 infrared spectrophotometer. The percentage of the amine group's acetylation in a sample is given by (A•655/A345o) x 155. Here, A•655 and A345o are the absorbances at 1650 cm -• and 3450 cm -•, •espectively. Solubility test. The solubility of water-soluble chitosans was determined by a method of Yalpani and Hall (38). The molecular weight, degree of deacetylation, and solubility of water-soluble chitosans used in these studies are listed in Table I. PREPARATION OF THE MOISTURE MASK Shown in Table II is the formula for the moisture mask, wherein 0.5% to 2.0% (w/v) water-soluble chitosans were used to replace the thickening agent (2.0% methyl cellu- lose). The buffer and the humectant were added to the water and heated at 70-80øC, and then the thickening agent and the film-forming agent were added and mixed well to form the aqueous phase at 70ø-80øC. The preservative and the surfactant were added to ethyl alcohol to obtain the oil phase at 70ø•80øC. The oil phase was poured into the aqueous phase and homogenized to obtain the product. CHARACTERIZATION OF THE PREPARED MOISTURE MASK Viscosity of the moisture mask. A 5-ml aliquot of moisture mask was placed onto a cone/ plate cell (pk 45) that was maintained at 25øC. Viscosity measurements were performed at shear rates of 0•100 s -t with a Haake Viscometer CV20 (Haake Mess-Technik Gmbh. Co., Germany). Absorbance test. The absorbance at 490 nm of the prepared moisture mask was measured by a spectrophotometer (Spectrophoto U-200, Hitachi Co., Japan) to be used as an index of moisture mask color. Table I Molecular Weight, Degree of Deacetylation, and Solubility of Water-Soluble Chitosans Prepared at Various Sonication Times at 300 W and 4 ø _+ 0.2øC Sonication time (min) Molecular weight Degree of Solubility (x 10 6 Da) deacetylation (%) in water (g/dl) U3 chitosan 2.42 83.2 0.955 a U30 chitosan 1.62 82.9 0.965 a U120 chitosan 1.17 84.2 0.966 a Values (n = 3) followed by the same superscript within the same column are not significantly different (p , 0.05 by Duncan's multiple range test). U3, U30, and U120 chitosans were obtained by ultrasonic treatment on a chitosan acetic acid solution for 3, 30, and 120 min, respectively, after which they underwent dialysis and freeze drying.

MOISTURE MASKS AND CHITOSANS 5 Table II Formula for Moisture Mask Ingredients Chemicals Percentage (%) Film-forming agent Polyvinyl alcohol 15.0 Thickening agent Methyl cellulose 2.0 Humectant 1-3 butadiene 5.0 Alcohol Ethyl alcohol 12.0 Preservative Methylparaben 0.4 Buffer Sodium citrate q.s. for pH 6.2-6.4 Surfactant Polyoxyethylene 20 oleyl ether 0.5 Water q.s. 100 Saj•ty test. The safety of the product was tested in terms of sensitivity of shaved rabbit (NZW) skin. A 0.1-g aliquot of prepared moisture mask was evenly applied to an approximately 9-cm 2 patch of shaved rabbit skin. Rabbits were kept in an air- conditioned room (25 ø + 0.5øC and 50-60% RH). The sensitivity of the rabbit skin was evaluated by the Draize scoring method (39). Water-holding capacity test. The water-holding capacity of the skin was tested by the corneometer method (40-42). The corneometer measures changes of electrical capaci- tance that are related to the moisture contents of the skin before and after applying the moisture mask. A 0.2-g aliquot of moisture mask was evenly applied to ca. a 25-cm 2 patch on the volar forearm of seven healthy volunteers who were fully informed of the nature of the study and the procedure involved in a test room of 75% RH and 20 ø + 0.5øC. Changes of electrical capacitance were recorded over time with a skin analyzer SHP88 (sebumeter + corneometer + pH-meter, Courage & Khazaka, Germany) ran- domly at eight points. Every sample measurement was repeated three times. The ca- pacitance increase ratio is expressed as: electrical capacitance after moisture mask applied Capacitance increase ratio = electrical capacitance of skin without moisture mask Original electrical capacitances were between 13.4 and 14.2 corneometer units. Film-formation time. A 0.2-g aliquot of moisture mask was applied to an approximately 25-cm 2 patch on the volar forearm of seven healthy volunteers (who were fully informed of the nature of the study and the procedure involved) in a test room of 75% RH and 20 ø + 0.5øC to observe the time needed for film formation by an experienced person. RESULTS VISCOSITY OF MOISTURE MASKS Results in Figure 1 show the apparent viscosities of the moisture masks measured at 10 -1 s to be 5.4x 103 4.5 x 103 , and 4.0x 10 .3 cp for those containing 2% 1% and 0.5% water-soluble chitosans, respectively. The apparent viscosity decreased to 1.8 x 103, 0.5 x 103, and 0.1 x 103 cp, respectively, when they were sheared at 100 s-•. The results show that moisture masks containing water-soluble chitosans were shear-thinning so-