INTRODUCTION The concentration of iodine species can be measured using several different analysis methods 1-3 . One of the most well- known methods involves iodine titration with a thiosulfate solution 4,5 . Total iodine can be analyzed using spectrometry, such as inductively coupled plasma-atomic emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS) and inductively coupled plasma-mass spectrometry (ICP-MS) 3,6,7 . As elemental iodine has various valance states, various stable iodine species are present in aqueous solutions. Stable iodine species can include iodide ions, triiodide ions, iodine and iodate ions. For the quantitative analysis of these species, ion chromatography (IC) has been used in analytical laboratories 3 . In addition, ultraviolet-visible spectrophotometry and Raman spectrometry have been used for the speciation and quantitative analyses of iodine species 8,9 . Recently, after the severe accident at the Fukushima nuclear power plant in Japan, the chemical behaviour of radioactive iodine received increased attention as a result of interest in evaluating the volatility of iodine species, which depends on the chemical conditions of the exposed environ- ments. The use of γ-ray spectroscopy to measure radioactivity is the best method for determining radioactive iodine concentrations. However, to use radioactive iodine, a licensed Determination of Triiodide Ion Concentration Using UV-Visible Spectrophotometry† SANG-HYUK JUNG 1,2 , JEI-WON YEON 1,* , YONG KANG 2,* and KYUSEOK SONG 1 1 Nuclear Chemistry Research Division, Korea Atomic Energy Research Institute, Daedeokdaero 989-111, Yuseong-gu, Daejeon 305-353, Republic of Korea 2 School of Chemical Engineering, Chungnam National University, Daehakro 99, Yuseong-gu, Daejeon 305-764, Republic of Korea *Corresponding authors: E-mail: yeonysy@kaeri.re.kr; kangyong@cnu.ac.kr Published online: 23 June 2014; AJC-15415 The concentration of triiodide ions was determined using UV-visible spectrophotometry. The maximum absorption λmax for the analysis of triiodide ions were observed at 288 and 351 nm, with molar absorptivity values of 2.65 × 10 4 and 1.72 × 10 4 L cm -1 mol -1 , respectively. The absorbance of triiodide ions had little effects on the solution pH in the range of 2.0 to 6.5. However, the absorbance strongly depended on the iodide ion concentration. Consequently, we confirmed that triiodide ion concentrations in the range of 0.005-0.1 mM could be determined using UV-visible spectrophotometry. Keywords: Triiodide ion, UV-visible spectrophotometry, Iodide ion, Solution pH. †Presented at 5 th International Symposium on Application of Chemical and Analytical Technologies in Nuclear Industries (Nu-ACT 2013), Daejeon, Korea laboratory equipped with numerous radioactivity safety devices is generally required. Therefore, many researchers have performed their experiments using non-radioactive iodine under γ-ray radiation instead of radioactive iodine 10 . In this case, the analysis of iodine species should be performed by chemical methods. Similar to radioactive iodide ions, which are stably soluble in aqueous solution, non-radioactive iodide ions can also be oxidized into volatile iodine under γ-ray radiation.Under the selected experimental conditions, the iodide ion concentration is relatively high, allowing the oxidized species, molecular iodine,to react with iodide ions and form triiodide ions, which are the more stable soluble species. Therefore, it is important to measure the concentration of triiodide ions to evaluate the volatility of iodine species. In the present work, we established a simple method to analyze the triiodide ion concentration using UV-visible spectrophotometry. First, we identified distinct absorption wavelengths and determined the maximum absorbance for the analysis of triiodide ions. Second, the absorbance of triiodide ions was confirmed to be independent of the solution pH. Third, we evaluated the effect of iodide ions on the formation of triiodide ions by analyzing the UV-visible absorption spectra. Lastly, the detection range of triiodide ions was determined for the UV-visible spectrophotometric method. ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY Asian Journal of Chemistry; Vol. 26, No. 13 (2014), 4084-4086 http://dx.doi.org/10.14233/ajchem.2014.17720