COSMETIC FORMULATIONS WITH ARGIRELINE® 161 a wavelength of 260 nm, at which absorption of the active principle is maximal. The same formulation with no active principle was assayed as a control. Diffusion across a membrane. Most published studies involve Franz-type cells (17-19). The FDC-400 cell (Vidra-Foe, Barcelona, Spain) consists of two compartments with a membrane clamped between the donor and receiver chambers. As the receptor phase we used a phosphate-buffered solution at pH 5 .6 (normal skin pH). Three types of mem­ brane (all 47 mm in diameter with 0.45-µm pore size) were tested: methylcellulose, nylon, and polysulfone (supplied by Millipore, Madrid, Spain). The concentration of Argireline® in the receptor cell was measured by UV­ spectrophotometry at 260 nm (A.max). The method was previously validated and verified for accuracy, precision, and linearity (20). A Perkin Elmer UV/Vis Lambda 40 UV­ spectrophotometer was used for all measurements. RESULTS AND DISCUSSION The data are given as the mean and standard deviation of six determinations made with samples of each formulation at each temperature and after each storage period. All results were compared by analysis of variance (ANOV A) for a 95 % confidence level to identify significant differences. ORGANOLEPTIC CHARACTERISTICS Tables II and III show the changes in organoleptic properties with time in the gel and cream formulations, respectively. The temperature or duration of storage did not sig­ nificantly affect the external appearance or texture of either formulation after 12 months. After 30 days, refrigerated samples showed better consistency than samples stored at room temperature. Consistency tended to decrease in the gel formulation after 12 months, with no differences between samples stored under refrigeration or at room Table II Changes in Organoleptic Characteristics of the Gel Formulation During Storage Storage conditions Organoleptic characteristics Time Temp. (°C) Color Texture Odor Consistency Exudate 0 days 4 Transparent Smooth, thin, cool Noticeable Viscous, easy No to spread 25 Transparent Smooth, thin Noticeable Viscous, easy No to spread 30 days 4 Unchanged Unchanged Unchanged Unchanged No 25 Unchanged Unchanged Unchanged Thinner No 60 days 4 Unchanged Unchanged Unchanged Unchanged No 25 Unchanged Unchanged Unchanged Unchanged No 90 days 4 Unchanged Unchanged Unchanged Unchanged No 25 Unchanged Unchanged Unchanged Unchanged No 6 months 4 Unchanged Unchanged Unchanged Unchanged No 25 Unchanged Unchanged Unchanged Unchanged No 12 months 4 Unchanged Unchanged Change Decrease Yes 25 Unchanged Unchanged Change Decrease Yes

162 JOURNAL OF COSMETIC SCIENCE Table III Changes in Organoleptic Characteristics of the Cream Formulation During Storage Storage conditions Organoleptic characteristics Time Temp. (°C) Color Texture Odor Consistency Exudate 0 days 4 White Smooth, creamy Noticeable Viscous, easy No to spread 25 White Smooth, creamy Noticeable Viscous, easy No to spread 30 days 4 Unchanged Unchanged Unchanged Viscous, harder No 25 Unchanged Unchanged Unchanged Viscous, softer No 60 days 4 Unchanged Unchanged Unchanged Unchanged No 25 Unchanged Unchanged Unchanged Unchanged No 90 days 4 Unchanged Unchanged Unchanged Unchanged No 25 Unchanged Unchanged Unchanged Unchanged No 6 months 4 White Smooth, creamy Unchanged Viscous, harder No 25 White Smooth, creamy Unchanged Viscous, harder No 12 months 4 White Creamy, hard Unchanged Viscous, harder, Yes crust formation 25 White Smooth, creamy Unchanged Viscous, harder No temperature. In the cream formulation, consistency increased after six months, and a crust had formed after storage for 12 months at 4 °C. pH The data in Table IV show that pH was acidic in both of the freshly made up formu­ lations, but was higher in the gel than in the cream. No significant changes over time were seen in either formulation regardless of storage temperature, a finding that makes these formulations suitable for topical application (only in regard to pH value). RHEOLOGICAL CHARACTERISTICS Rheological assays to measure viscosity under different storage conditions and at differ­ ent times indicated that both formulations showed pseudoplastic behavior. Figures 1 and 2 plot the mean values for the cream formulation after 24 h, seven days, and 30 days of storage at 4 ° C and 25 ° C, respectively. Storage temperature had no significant effect on Table IV Changes in pH During Storage Time (days) pH 0 30 60 90 Gel 4 ° c 6.18 6.1 6.18 6.12 25 ° c 6.36 6 6.25 6 Cream 4 ° c 4.1 4 4.2 4.1 25 ° c 3.92 4 3.95 4.05