210 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS each other, will change considerably when they are dissolved in selected liquid emol- lients (4). The present study (5) was undertaken to determine the influence of 12 cosmetic and related solvents of varying polarity on the UV absorption characteristics of 13 sunscreen chemicals in order to aid the cosmetic chemist in achieving a better understanding of the interactions that are possible between UV absorbers and liquid components used in sunscreen formulations. EXPERIMENTAL MATERIALS Thirteen sunscreen chemicals which are widely used in cosmetic formulations were tested. The list included five UVA (320 to 360 nm) absorbers (i.e., menthyl anthrani- late, oxybenzone, dioxybenzone, sulisobenzone, and butylmethoxy dibenzoylmethane) and eight UVB (290 to 320 nm) absorbers (i.e., PABA, ethyl dihydroxypropyl PABA, octylcyano diphenylacrylate, octyl methoxycinnamate, octyl salicylate, homomenthyl salicylate, octyl dimethyl PABA, and triethanolamine salicylate). All of the sunscreens tested, with the exception of butylmethoxy dibenzoylmethane, have been assigned Cat- egory 1: safe and effective status by the FDA over-the-counter review panel (6). Twelve solvents were also selected for study, based upon either their usage in cosmetic formulation or their polarity, and are listed in Table I in decreasing order of polarity in accordance with Vaughan's solubility parameter assignments (7). Chromatographic analysis was performed on all sunscreens and solvents used in the study in order to confirm their purity. Our assays showed that the materials used were well within the purity specified by the supplier (i.e., not less than 98%). METHODOLOGY Solutions for UV spectral analysis were accurately prepared using sunscreen-solvent Table I Solvents and Their Corresponding Solubility Parameters Listed in Decreasing Order of Polarity Solubility parameter Solvent at 25øC Ethanol 70%-water 30% 16.0 Propylene glycol 14.0 Ethanol 90%-water 10% 13.9 Ethanol 12.8 Hexylene glycol 12.3 Methyl carbitol 10.7 Ethoxyethanol 10.6 Isopropyl myristate 8.0 Isopropyl palmitate 7.8 C•2-C•5 alcohols benzoate 7.6 Hexane 7.3 Mineral oil 7.0

SOLVENTS AND SUNSCREEN ABSORBANCE 211 combinations where the solubility of the sunscreen was possible in the solvent at room temperature. A 50 mg _+ 1 mg sample of each sunscreen was weighed accurately into a 100-ml volumetric flask and then diluted to the mark with solvent. The resulting stock solution was then diluted 1:100 to yield a final sunscreen concentration of 5 mg/L. UV absorbance curves of each final dilution were obtained with the aid of a Perkin- Elmer Lambda 4B UV/VIS spectrophotometer. A background correction was performed using 1-cm quartz cells filled with blank solvent. The UV absorbance curve was then recorded by scanning wavelengths between 200 and 400 nm, using a sample of the final dilution in the 1-cm quartz cell. The wavelength of maximum absorbance (• max) and the corresponding absorbance value were determined and displayed by the micropro- cessor unit of the spectrophotometer. The spectrophotometer's wavelength accuracy is _+ 0.3 nm and its absorbance accuracy is -+0.005 A when measured at 1,000 absorbance unit (A). A holmium chloride standard cell was used to calibrate the spectrophotometer and its microprocessor unit. Our results were within the specifications established for the standard cell and the spectrophotometer. The molar absorptivity (½) was calculated for each test solution at the wavelengths of maximum absorbance (• max) in the ultraviolet regions (UVA, UVB, and UVC). How- ever, only the values in the UVA and UVB regions are reported in this paper (8). RESULTS The ultraviolet absorption spectral properties (X max and ½ values) of 13 sunscreen chemicals in various polar, semi-polar, and non-polar solvents were obtained. These data are summarized in Tables II-IV as three separate groups of compounds. Sun- screens where the • max is shifted towards shorter wavelengths (hypsochromic or blue Table II UV Spectral Data of Sunscreen Chemicals Showing Hypsochromic Shifts in the •. max PABA Solvent }, max Dioxybenzone Sulisobenzone Oxybenzone max ½ •. max ½ •. max ß Ethanol 70%-water 30% 266 13,600 326 9,400 324 8,600 321 9,300 Propylene glycol 272 14,500 326 9,100 324 7,500 322 8,400 Ethanol 90%-water 10% 271 13,800 326 9,400 325 8,900 324 9,500 Ethanol 272 13,100 327 9,300 326 8,400 325 9,400 Hexylene glycol 268 13,400 329 7,600 331 7,000 327 8,200 Methyl carbitol 291 18,300 324 8,900 333 5,600 323 8,400 Ethoxyethanol 293 18,900 325 9,600 334 8,500 327 9,000 Isopropyl myristate ins. ins. 352 10,600 ins. ins. 328 9,000 Isopropyl palmirate ins. ins. 351 10,200 ins. ins. 327 9,000 C•2-C•5 alcohols benzoate ins. ins. 352 9,900 ins. ins. 328 8,300 Hexane ins. ins. 351 13,100 ins. ins. 328 8,800 Mineral oil ins. ins. 352 11,400 ins. ins. 329 7,800 Wavelength shift from non-polar to polar solvent Ah max = Ah max = Ah max = Ah max = -27nm -26nm -10nm -8nm