Talanta 70 (2006) 174–177 Ion-exclusion chromatography with the direct UV detection of non-absorbing inorganic cations using an anion-exchange conversion column in the iodide-form Masanobu Mori a,∗ , Hideyuki Itabashi a , Mikaru Ikedo b , Kazuhiko Tanaka c a Faculty of Engineering, Gunma University, 1-5-1, Tenjin-cho, Kiryu, Gunma 376-8515, Japan b Graduate School of Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan c Graduate School for International Development and Cooperation, Hiroshima University, 1-5-1 Kagamiyama, Higashi-Hiroshima 739-8529, Japan Received 27 September 2005; received in revised form 10 January 2006; accepted 30 January 2006 Available online 10 March 2006 Abstract An ion-exclusion chromatographic method for the direct UV detection of non-absorbing inorganic cations such as sodium (Na + ), ammonium (NH 4 + ) and hydrazine (N 2 H 5 + ) ions was developed by connecting an anion-exchange column in the I - -form after the separation column. For example, NH 4 + is converted to a UV-absorbing molecule, NH 4 I, by the anion-exchange column in the I - -form after the ion-exclusion separation on anion-exchange column in the OH - -form with water eluent. As a result, the direct UV detection of Na + , NH 4 + and N 2 H 5 + could be successfully obtained as well as the well-resolved separation. The calibration graphs of the analyte cations detected with UV at 230 nm were linear in the range of 0.001–5.0 mM. The detection limits at S/N = 3 of the cations were below 0.1 M. This method was applied to real water analysis, the determination of NH 4 + in river and rain waters, or that of N 2 H 5 + in boiler water, with the satisfactory results. This could be applied also to low- or non-absorbing anions such as fluoride or hydrogencarbonate ions by the combination of a weakly acidic cation-exchange resin in the H + -form as the separation column and the anion-exchange conversion column. © 2006 Elsevier B.V. All rights reserved. Keywords: UV detection; Ammonium ion; Hydrazine ion; Ion-exclusion chromatography; Anion-exchange; Water analysis 1. Introduction Ion-exclusion chromatography has been the one of conve- nient way to determine weakly basic cations such as ammonium ion (NH 4 + ) or weakly acidic anions such as hydrogencarbonate ion (HCO 3 - ) [1–5]. The separations are obtained using an anion- exchange resin column in the OH - -form for the cations and a cation-exchange resin column in the H + -form for the anions only with water eluent, due to the penetration effect to the stationary phase. Conductivity has been commonly used as the detection method. However, the responses of partially ionized species such as NH 4 + (pK b = 4.75) and HCO 3 - (pK a = 6.34) are low due to the low limiting equivalent ionic conductance [6]. The spectrophotometric detector (e.g., UV detector) can sim- ply monitor ion species alternating to conductivity, since it ∗ Corresponding author. Tel.: +81 277 30 1271; fax: +81 277 30 1271. E-mail address: m mori@chem.gunma-u.ac.jp (M. Mori). can selectively change by changing the wavelength monitored. Commonly, the analyte ions monitored by UV detector are UV-absorbing ions such as nitrate or iodide ions at the wide wavelength. For non-UV-absorbing ions, the indirect detection and/or postcolumn derivatization with subsequent UV measure- ment has been considered to be the common detection method [7]. In indirect UV-detection, the eluent having absorbance in the UV spectral region is used for the detection of non-absorbing analyte ions [8–10]. A decrease of the signal is resulted in when a sample peak is eluted. However, this method is gen- erally used only in cases where the separation and detection conditions have been carefully worked out. In the postcolumn method, the ideal color-forming reagent is used in order to react with a large number of metal ions or inorganic anions. Basi- cally, the color-forming reagents used after ion chromatographic separations are aromatic dyes such as arenazo III [11] or 4-(2- pyridylazo)-resorsinol (PAR) [12] for metal ions, and chelate reagents such as ferric perchlorate [11] or ehylenediaminete- traacetic acid (EDTA) [13] for anions. The eluent concentration 0039-9140/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2006.01.043