Analytical Sciences

Ion-exclusion/cation-exchange Chromatography with Dual Detection of the Conductivity and Spectrophotometry for the Simultaneous Determination of Common Inorganic Anionic Species and Cations in River and Wastewater

Nobutake NAKATANI,*1,*2 Daisuke KOZAKI,*2 Masanobu MORI,*3 Kiyoshi HASEBE,*4 Nobukazu NAKAGOSHI,*2 and Kazuhiko TANAKA*2

*1 Department of Biosphere & Environmental Sciences, Faculty of Environmental Systems, Rakuno Gakuen University, 582 Bunkyodai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan
*2 Graduate School for International Development and Cooperation, Hiroshima University, 1-5-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8529, Japan
*3 Graduate School of Engineering, Gunma University, 1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan
*4 Faculty of Human Life Sciences, Fuji Women’s University, Hanakawa, Ishikari, Hokkaido 061-3204, Japan

Simultaneous determinations of common inorganic anionic species (SO₄²⁻, Cl⁻, NO₃⁻, phosphate and silicate) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) were conducted using an ion-chromatography system with dual detection of conductivity and spectrophotometry in tandem. The separation of ionic species on a weakly acidic cation-exchange resin was accomplished using a mixture of 100 mM ascorbic acid and 4 mM 18-crown-6 as an acidic eluent (pH 2.6), after which the ions were detected using a conductivity detector. Subsequently, phosphate and silicate were analyzed based on derivatization with molybdate and spectrophotometry at 700 nm. The detection limits at S/N = 3 ranged from 0.11 to 2.9 μM for analyte ionic species. This method was applied to practical river water and wastewater with acceptable criteria for the anion-cation balance and comparisons of the measured and calculated electrical conductivity, demonstrating the usefulness of the present method for water quality monitoring.

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