]. Cosmet. Sci.) 57, 377-383 (September/October 2006) A novel volumetric method for quantitation of titanium dioxide in cosmetics YOUNG SO KIM, BOO-MIN KIM, SANG-CHUL PARK, HYE-JIN JEONG, and IH SEOP CHANG, Amore Pacific Corporation, R&D Center) 314-1 Bora-dong Giheung-gu Yongin-si Gyeonggi-do, 446-729 Korea. Accepted for publication April 4) 2006. Synopsis Nowadays there are many sun-protection cosmetics incorporating organic or inorganic UV filters as active ingredients. Chemically stable inorganic sunscreen agents, usually metal oxides, are widely employed in high-SPF (sun protection factor) products. Titanium dioxide is one of the most frequently used inorganic UV filters. It has been used as a pigment for a long period of cosmetic history. With the development of micronization techniques, it has become possible to incorporate titanium dioxide in sunscreen formulations without the previous whitening effect, and hence its use in cosmetics has become an important research topic. However, there are very few works related to quantitation of titanium dioxide in sunscreen products. In this research, we analyzed the amounts of titanium dioxide in sunscreen cosmetics by adapting redox titration, reduction of Ti(IV) to Ti(III), and reoxidation to Ti(IV). After calcification of other organic ingredients of cosmetics, titanium dioxide is dissolved by hot sulfuric acid. The dissolved Ti(IV) is reduced to Ti(III) by adding metallic aluminum. The reduced Ti(III) is titrated against a standard oxidizing agent, Fe(III) (ammonium iron(III) sulfate), with potassium thiocyanate as an indicator. In order to test the accuracy and applicability of the proposed method, we analyzed the amounts of titanium dioxide in four types of sunscreen cosmetics, namely cream, make-up base, foundation, and powder, after adding known amounts of titanium dioxide (1 - 25 w/w%). The percentages of titanium dioxide recovered in the four types of formulations were in the range between 96% and 105%. We also analyzed seven commercial cosmetic products labeled with titanium dioxide as an ingredient and compared the results with those obtained from ICP-AES (inductively coupled plasma-atomic emission spectrometry), one of the most powerful atomic analysis techniques. The results showed that the titrated amounts were well in accord with the analyzed amounts of titanium dioxide by ICP-AES. Although instrument-based analytical methods, namely ICP-MS (inductively coupled plasma-mass spectrometry) and ICP-AES, are best for the analysis of titanium, it is difficult for small cosmetic companies to install such instruments because of their high cost. It was found that the volumetric method presented here gives quantitatively accurate and reliable results with routine lab-ware and chemicals. INTRODUCTION The sun is a source of energy in every living organism on earth. However, some portions of the electromagnetic radiations from the sun can be harmful. Since UV radiation (UVA, UVB, and UVC) has very high energy, too much skin exposure to the sun's radiation can be dangerous. Most UV electromagnetic radiation from the sun is filtered 377

378 JOURNAL OF COSMETIC SCIENCE by the ozone layer and absorbed in the atmosphere of the earth. Only a small percentage of UV radiation can reach the surface of the earth: 0.1 % of UVB (290-320 nm) and 4.9% of UV A (320-400 nm). Most energetic UVC (below 290 nm) is filtered com­ pletely by the ozone layer and does not reach the earth's surface. Shorter-wavelength UVB is more energetic than UVA. UVB's high energy can cause severe erythema and skin cancer and sometimes brings about DNA and RNA mutation. UVB is also known to be responsible for skin thickening that leads to skin aging. Although longer­ wavelength UVA rays are less energetic than those of UVB, the irradiance amounts of UVA within terrestrial sunlight are 100 times greater than that of UVB. In addition, UVA can more easily penetrate stratum corneum, as well as water, glass, and cotton. UVA has been shown to cause immediate tanning, photosensitizing, and photoaging. Repeated exposure can lead to erythema. (1). For these reasons, sun protection has become one of main market categories for beauty care products. Thus there are many commercial sun-protection cosmetics on the market containing organic or inorganic sunscreen agents. Organic sunscreen agents are conjugated aromatic chromophores, such as octyl methoxy­ cinnamate, p-amino benzoic, octyl salicylate, homosalate, methoxydibenzylmethanes, benzophenone derivatives, menthyl anthranilates, and camphor derivatives. These mol­ ecules go to an excited state by absorbing high-energy UV rays, and return to their ground state by emitting longer-wavelength low-energy rays (2). Each organic UV absorber has a specific wavelength range for which it offers protection. Chemically stable and inert inorganic sunscreens, usually metal oxides, are widely em­ ployed in high-SPF products (3 ). They protect skin from the sun by reflecting, diffract­ ing, and sometimes absorbing UV radiation (4). These metal oxides have many advan­ tages. They can protect from both UVA (320-400 nm) and UVB (290-320 nm) effectively and can impart high SPF values at relatively low concentration levels. Most of all, they are less allergenic than organic sunscreens. One of the most frequently used inorganic UV filters is titanium dioxide. Titanium dioxide has been used as a pigment for a long period of cosmetic history. With the development of micronization tech­ niques, it has become possible to incorporate titanium dioxide in sunscreen formulations without the previously experienced whitening effect, and hence its use in cosmetics has become an important research topic (5 ,6). However, in point of analytical research, there are very few works related to quantitation of titanium dioxide in sunscreen products. In this article, we investigate ways to quantify titanium dioxide in cosmetics by titration. To examine the feasibility of the proposed method, we compared the results with data from an instrument-based analysis tech­ nique, ICP-AES. MATERIALS AND METHODS SAMPLES Cosmetics (cream, make-up base, foundation, and powder) containing 1 %, 5%, 10%, and 25% of titanium dioxide, were separately prepared. Commercial cosmetics were purchased from the market.