PERCUTANEOUS ABSORPTION OF SURFACTANTS 265 Air pump T 20% NaOH solution solution T T , T Saturated Flow Closed plastic 50% monoethanolamine NaCl meter container methanol solution (300m•/min) (3•) Figure 1. Schematic diagram showing 14CO2 collection in expired air. MEASUREMENT OF EXPIRATORY EXCRETION Carbon dioxide in the expiratory excretion was absorbed in 50% monoethanolamine- methanol solution (15 ml, 2 traps). Radioactivity was measured in the whole solution. This system gave a recovery of 14CO2 not less than 99%. MEASUREMENT OF EXCRETION IN FECES AND URINE This experimental system could not provide for separation of feces from urine thus, the feces and urine samples were jointly, respectively dried, combusted, and counted. MEASUREMENT OF THE AMOUNT REMAINING IN THE SKIN APPLICATION SITE •4C activity in the excised skin was extracted by methanol solution and then by toluene. •4C activity remaining in the extracted skin was measured by combustion of the skin after drying. ANALYSIS OF •4C All samples were counted with a Beckman LS-233 liquid scintillation spectrometer. Monoethanolamine-CO2 and extracted solution were dissolved in a liquid scintillator (5 gr. ppo, 0.1 gr. popop in 1 I toluene) for radioactivity measurement. Samples of body homogenate, feces and urine, and skin were combusted on a Sample Oxidizer (Packard Tri-carb, Model 306) to prepare for liquid scintillation counting. RESULTS AND DISCUSSION PERCUTANEOUS ABSORPTION OF LAEO Table I summarizes the intravital amount, fecal and urinary excretion, expiratory excretion, and percutaneous absorption four hours after the topical application of

266 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Amount of Percutaneous Absorption of LAEO Four Hours After Application Intravital Fecal and Expiratory LAEO Amount Urinary Excretion Excretion Percent Absorbed Lauryl Alcohol 17.7 + 1.9 1.2 + 0.2 27.2 + 1.0 LAEO-1 22.9 + 1.9 17.1 + 0.7 16.1 + 1.8 -- LAEO-2.6 15.6 _+ 0.6 40.8 _+ 3.2 4.8 _+ 0.5 -- LAEO-6.4 10.4 _+ 0.3 16.4 _+ 2.4 1.0 _+ 0.2 -- LAEO-10 2.1 _+ 0.1 2.5 + 0.4 0.3 + 0.02 46.1 + 0.9 56.1 _ 4.2 61.2 + 2.8 27.8 + 2.8 4.9 _ 0.4 Applied dose: 1.38 •mole/25 •1 ethanol (1.0 •Ci). Dorsal skin of hairless mouse: 2.9 cm 2. The values are expressed as percent of the applied quantity. LAEO. Table II shows the amount of the percutaneous absorption, the amount remaining in the applied skin, and the sum of these or recovery rate in this experimental system. Table II Recovery Rate in This Experimental System Percent Retained Sample Name Percent Absorbed by the Excised Skin Percent Recovery Lauryl Alcohol 46.1 _+ 0.9 52.9 + 2.0 98.5 -+ 1.5 LAEO-1 56.1 + 4.2 43.5 -+ 6.0 99.3 -+ 2.2 -- LAEO-2.6 61.2 + 2.8 40.5 _+ 2.8 101.3 + 2.6 -- LAEO-6.4 27.8 + 2.8 71.8 + 2.0 99.7 + 1.4 -- LAEO-10 4.9 -+ 0.4 95.7 + 0.9 100.6 _+ 1.2 Applied dose: 1.38/xmole/25/xl ethanol (1.0/xCi). Dorsal skin of hairless mouse: 2.9 cm 2. The values are expressed as percent of the applied quantity. It can be seen from the recovery pattern that the method used allows reliable and reproducible measurement of percutaneous absorption. The data clearly show that LAEO-1 and LAEO-2.6 penetrate the skin readily, while LAEO-10 is barely absorbed. MEASUREMENT OF PERCUTANEOUS ABSORPTION RATE OF LAEO In order to obtain the rate of percutaneous absorption of LAEO, changes in absorption with time for the various LAEO were determined (Figure 2). Each exhibited linearity after a slight time lag. The rates obtained from the slopes of these lines are shown in Table III. Lauryl alcohol was the fastest followed by LAEO-2.6 and LAEO-1. LAEO-10 had a slower rate by one order of magnitude. MEASUREMENT OF PERCUTANEOUS ABSORPTION RATE FROM EXPIRATORY EXCRETION We also followed the percutaneous absorption rate from expiratory excretion by measuring •4CO2 in the expired air over a period of time after percutaneous absorption of •4C-LAEO. The time rate of change of the percent •4CO2 expired for each LAEO is