ORIGINAL PAPER Particle size characterization of titanium dioxide in sunscreen products using sedimentation field-flow fractionation–inductively coupled plasma–mass spectrometry Atitaya Samontha & Juwadee Shiowatana & Atitaya Siripinyanond Received: 29 July 2010 / Revised: 2 October 2010 / Accepted: 4 October 2010 / Published online: 16 October 2010 # Springer-Verlag 2010 Abstract Sedimentation field-flow fractionation–inductively coupled plasma–mass spectrometry (SdFFF-ICP-MS) was successfully applied to investigate particle size distribution of titanium dioxide (TiO 2 ) in sunscreen samples after hexane extraction to remove organic components from the samples. Three brands of sunscreen products of various sun protection factor (SPF) value were used as samples. Different particle size distribution profiles were observed for sunscreen samples of various brands and SPF values; however, the particle size distributions of titanium dioxide in most sunscreen samples investigated in this work were larger than 100 nm. The titanium dioxide concentrations were higher for the products of higher SPF values. By comparing the results obtained from online SdFFF-ICP-MS and those from the off- line ICP-MS determination of titanium after acid digestion, ICP-MS was found to effectively atomize and ionize the titanium dioxide particle without the need for acid digestion of the samples. Therefore, the online coupling between SdFFF and ICP-MS could be effectively used to provide quantitative information of titanium dioxide concentrations across particle size distribution profiles. Keywords Titanium dioxide . Sunscreen . Particle size . Sedimentation field-flow fractionation . Inductively coupled plasma–mass spectrometry Introduction Ultraviolet (UV) radiation including UV-A (320–400 nm) and UV-B (290–320 nm) can cause skin cancer and other harmful effects to humans [1–4]. To avoid unwanted skin effects from the sun it is necessary to use sunscreen filters. Titanium dioxide (TiO 2 ), which is a physical UV filter, can reflect and scatter UV radiation very efficiently [5], and it is, therefore, often used to formulate sunscreen products with a high sun protection factor (SPF) value [6]. Accord- ing to the European legislation, titanium dioxide is the only inorganic UV filter permitted to be used in sunscreen products with the maximum allowable concentration of 25% (w/w)[7]. The radiation reflection and scattering efficiencies of titanium dioxide depend on its concentration and particle size, with a particle size of approximately 60– 120 nm the most effective in UV reflection and scattering ability [5]. Therefore, the analysis of sunscreen cosmetics in terms of the concentration and particle size of titanium dioxide should be considered. Although the official methods for determining titanium dioxide particles in sunscreen cosmetics, either in terms of quantitative element content or the particle size distribution, have never been documented, several analytical techniques have been reported for determination of titanium dioxide in sunscreen. These techniques include the classical volumet- ric method [8], atomic absorption spectrometry [9], induc- tively coupled plasma optical emission spectrometry [8, 10], and X-ray fluorescence spectrometry [11, 12]. For particle size characterization, flow field-flow fractionation (FlFFF) has been reported for titanium dioxide particles in a commercial sunscreen product [13] and titanium dioxide nanoparticles imprinted for tyrosine [14]. A. Samontha : J. Shiowatana : A. Siripinyanond (*) Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand e-mail: scasp@mahidol.ac.th Anal Bioanal Chem (2011) 399:973–978 DOI 10.1007/s00216-010-4298-z