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

212 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table III UV Spectral Data of Sunscreen Chemicals Showing Little or No Shift in the X max Triethanolamine Octyl Homomenthyl Menthyl salicylate salicylate salicylate anthranilate Solvent X max E }x max E • max e • max e Ethanol 70%-water 30% 298 2,800 308 4,900 306 4,800 336 5,600 Propylene glycol 298 2,100 307 4,800 307 3,700 335 4,800 Ethanol 90%-water 10% 297 3,000 305 4,000 305 4,300 337 5,000 Ethanol 298 2,900 307 4,200 306 4,600 338 5,000 Hexylene glycol 298 2,200 306 3,900 306 2,300 339 4,800 Methyl carbitol 301 3,100 309 4,000 307 4,800 338 5,700 Ethoxyethanol 301 3,000 310 4,000 307 4,700 339 5,600 Isopropyl myristate ins. ins. 309 4,200 308 5,100 338 4,600 Isopropyl palmitate ins. ins. 308 4,600 307 5,000 337 4,700 C12-C•5 alcohols benzoate ins. ins. 309 3,900 308 4,900 337 6,200 Hexane ins. ins. 310 4,100 308 5,100 334 5,400 Mineral oil ins. ins. 310 4,200 308 4,500 334 6,000 Wavelength shift from A•. max = A•. max ---- A•. max ---- A•. max = non-polar to polar -- 3 nm -- 2 nm -- 2 nm q- 2 nm solvent shift) in going from non-polar to polar solvents are listed in Table II. Sunscreens that experienced little or no shift in their }t max in the various solvents tested are listed in Table III. Sunscreens, where the }t max was shifted towards longer wavelengths (bathochromic or red shift), are listed in Table IV. Experimental values could not be obtained in those instances where the sunscreen was not soluble in the particular solvent selected for study and are so indicated in each table. The change in the wavelength of maximum absorbance (A }t max) from the least polar solvent (i.e., mineral oil) to the most polar solvent (i.e., ethanol 70%-water 30%) for each sunscreen is listed at the bottom of each table (II-IV). Where a sunscreen was insoluble in either a particular polar or non-polar solvent, the A }t max was calculated between the least polar solvent and the most polar solvent in which the sunscreen was soluble. In addition, selected UV absorption spectra of several of the more important sunscreen chemicals in each category (hypsochromic, bathochromic, and minimum or no shift), illustrating the magnitude of the shift in the }t max in both polar and non-polar sol- vents, are also presented in Figures 1-5. DISCUSSION CHANGES IN WAVELENGTH OF MAXIMUM ABSORBANCE In order for the cosmetic chemist to estimate the effect formulation components have on the UV characteristics of a particular sunscreen chemical, the polarity of the sunscreen and the polarity of the components in the preparation should be determined. The rela-