Talanta 87 (2011) 80–84 Contents lists available at SciVerse ScienceDirect Talanta jo u r n al hom epage: www.elsevier.com/locate/talanta In vitro monitoring of natural thorium in urine using fluorimeter S. Kalaiselvan a,∗ , A.R. Lakshmanan b , V. Meenakshisundaram a a Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India b Savitha Engineering College, Thandalam, Chennai 602 105, India a r t i c l e i n f o Article history: Received 18 June 2011 Received in revised form 15 September 2011 Accepted 16 September 2011 Available online 1 October 2011 Keywords: Bioassay Thorium Solvent extraction Fluorimetry a b s t r a c t A relatively less expensive and less time consuming radio analytical technique for quantitative determi- nation of Th nat in urine at mBq level is developed and reported in this paper. Th in urine is co-precipitated with Ca 3 (PO 4 ) 2 from wet oxidized urine matrix and the precipitate is dissolved in HNO 3 and evaporated to dryness. The residue is dissolved in 3 M HCl and 200 mg of Na-EDTA is added to mask Ca 2+ , Mg 2+ and Fe 3+ ions. Th 4+ is extracted into 0.01 M PC-88A (2-ethyl hexyl phosphonic acid mono-2-ethylhexyl ester), dissolved in toluene from the experimentally optimized pH 2.5 ± 0.3 in aqueous phase. Th 4+ is stripped into 8.0 M HCl and evaporated to dryness. The content of the beaker is dissolved in pH 1.8 HCl and com- plexed with 3-hydroxy flavone. The sample is excited at 397 nm and fluorescence intensity is measured at 462 nm. The detailed study of the method is presented in this paper. Interference study on elements that are normally present in urine and other actinides (if present) is also given. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Radiation workers who handle thorium are routinely monitored at predetermined intervals. After the intake, the majority of tho- rium that enters the body is excreted through the feces in the first 48 h and a small amount through the urine. Urine containing thorium undergoes systemic excretion whereas feces containing thorium undergoes both systemic and non-systemic excretions. Therefore, urinalysis is preferred for dose assessment. In addi- tion, the body also has a retention factor for thorium which drops rapidly [1]. Hence, sensitive and fast method is required to esti- mate thorium in urine. Sensitive techniques like ICPMS method with MDA 1.0 ng/l [2] and Neutron Activation Analysis (NAA) with MDA 0.01 ng/l [3] are very much suitable for low level estimation of natural thorium but are expensive. It is reported that alpha spec- trometric technique involving anion exchange separation requires seven days for completion of analysis with MDA 0.1 mBq/l [4]. Hence, an attempt is made to develop a sensitive and fast method for estimation of intake of thorium and the same is given in detail in this paper. This is a solvent extraction method of using PC-88A as extractant [5–7] and estimation of quantity using fluorimeter. Tho- rium is extracted into 2-ethyl hexyl phosphonic acid mono-2-ethyl hexyl ester (PC-88A) dissolved in toluene. In addition, fluorescent technique is also optimized to determine thorium at sub microgram ∗ Corresponding author. Tel.: +91 044 27480062; fax: +91 044 27480235. E-mail address: kalai@igcar.gov.in (S. Kalaiselvan). level by complexing with 3-hydroxy flavone dissolved in different polar solvents. 2. Experimental 2.1. Chemicals All chemicals used in the experiments including Th(NO 3 ) 4 ·4H 2 O were of analytical reagent grade. 2.2. Instrument Fluorolog-3 Jobin Yvon–Spex Spectrofluorimeter, New Jersey is used. Its spectral resolution is 0.2 nm. 2.3. Method The separation scheme for thorium from urine matrix is given with flow chart format in Fig. 1. The scheme essentially consists of three steps viz: (a) pre concentration, (b) solvent extraction sepa- ration and (c) fluorimetric estimation. 2.3.1. Pre-concentration To 1000 ml of each pooled urine sample, a known amount of Th at microgram level was spiked, stirred and heated with 50 ml of conc. HNO 3 , 25 ml of conc. HCl and 1 ml of H 2 O 2 until the solu- tion turns into pale yellow. Thorium is then co-precipitated with Ca 3 (PO 4 ) 2 by adjusting the pH of the sample to 9 using ammo- nia. The precipitate is centrifuged and dissolved in 10 ml of 8 M 0039-9140/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2011.09.044