Analytica Chimica Acta 713 (2012) 86–91 Contents lists available at SciVerse ScienceDirect Analytica Chimica Acta jou rn al hom epa ge: www.elsevier.com/locate/aca A novel approach for determining total titanium from titanium dioxide nanoparticles suspended in water and biosolids by digestion with ammonium persulfate Kambiz Khosravi ∗ , M. Ehsanul Hoque, Brian Dimock, Holger Hintelmann, Chris D. Metcalfe Water Quality Centre, Trent University, Peterborough, Ontario, K9J 7B8, Canada a r t i c l e i n f o Article history: Received 17 June 2011 Received in revised form 22 November 2011 Accepted 23 November 2011 Available online 1 December 2011 Keywords: Nanoparticles Titanium dioxide Digestion Fusion Ammonium persulfate ICP-MS a b s t r a c t Titanium dioxide (i.e. TiO 2 ) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO 2 nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO 2 as Ti 4+ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO 2 nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti 4+ from 6 g mL -1 aque- ous suspensions prepared from 10 g mL -1 suspension of different forms of TiO 2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot- plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL -1 , and the limit of quantification (LOQ) was 0.20 ng mL -1 . Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentra- tions of TiO 2 of 1.8 and 1.6 ng mL -1 for the wastewater samples, respectively, and 317.4 ng mg -1 dry weights for the biosolids. The reactions between persulfate ions and TiO 2 were evaluated using stoichio- metric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Nanoparticles are nanometer sized (1–100 nm) crystalline to amorphous materials [1]. These particles either originate naturally in the environment or are engineered. The engineered nanopar- ticles are manufactured and incorporated into nanomaterials for various uses in industry, medicine and in personal care products [2]. The characterization and quantification of engineered nanoparti- cles (NPs) in various matrixes is an area of active research because of concerns about the potential effects of exposure to NPs on humans and biota [3–6]. For NPs composed of metals or metal oxides, analytical tech- niques usually require digestion, followed by dissolution in aqueous media prior to analysis [7–9]. Currently, there are a wide variety of methods for digesting metals in environmental ∗ Corresponding author. Tel.: +1 705 748 1011. E-mail address: kambizkhosrav@trentu.ca (K. Khosravi). samples, such as open hot-plate, microwave and alkaline fusion. Microwave assisted and open hot-plate acid digestion methods are widely used techniques for preparing solid samples for analysis [10]. In these methods, the digestion is carried out with differ- ent combinations of mineral acids, such as: HNO 3 , HNO 3 + HCl, HNO 3 + HCl + HF, HNO 3 + HF, HNO 3 + HClO 4, and the fusion is carried out using Na 2 CO 3 , Na 2 CO 3 + Na 2 B 4 O 7 , LiBO 2 or LiB 4 O 7 [10,11]. Digestion of TiO 2 to yield Ti 4+ in environmental matrixes requires the use of particularly strong mineral acids, such as HF that is a health and safety hazard in the laboratory and sometime produces less than satisfactory recoveries [11]. Therefore, we devel- oped a method to digest TiO 2 in aqueous suspensions based on fusion of TiO 2 with ammonium persulfate, with heating on an open flame and further dissolution with dilute nitric acid. In the present study, we describe the optimization of this digestion technique for use with aqueous samples and compare recoveries to microwave digestion and open hot plate digestion using a tri-acid mixture (i.e. HNO 3 + HCl + HF). The reaction products were identified by FTIR and XRD, and a formula for the fusing reaction is proposed. The method 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.11.048