Simultaneous Measurement of Monovalent Cation Concentrations and Hydrogen Ion Concentration or Alkalinity in Environmental Waters by Ion Chromatography with Conductimetric Detection Using an ODS-Silica Column Modified with Lithium Dodecylsulfate

環境水の水質評価にとって重要な指標であるH^＋濃度又はアルカリ度（OH^−/HCO_3^−/CO_3^等）を共存する1価陽イオン類の濃度（Na^＋，NH_4^＋及びK^＋）と共に陽イオン交換作用を用いる簡便な導電率検出イオンクロマトグラフィーを用いて同時分析するため，ドデシル硫酸リチウムを修飾したODS-シリカ分離カラムを用い，0.1 mMドデシル硫酸リチウムを含む40 mM塩化リチウムと0.05 mM硫酸の混合溶離液（pH 4.0）を用いる方法について検討した。その結果，1価陽イオン類及びH^＋は，ドデシル硫酸基の有する陽イオン交換能により約15分以内で正のピークとして分離・検出できた。一方，アルカリ度は，酸・塩基中和反応による溶離液中のH^＋濃度の減少として，H^＋のピークの位置に負のピークとして検出できた。この最適分離条件下において，1価陽イオン類及びH^＋/アルカリ度の検量線，検出限界，再現性及び添加回収率について検討し，良好な結果を得た．本法を種々な酸性又はアルカリ性の実際水試料に対して適用したところ，種々な実際水試料のH^＋濃度及びアルカリ度の測定値は，本法と公定法の間で各々良好な相関性が認められた．このことから，本法の水質モニタリング法としての有用性が明らかとなった。Both H^+ and alkalinity are important key parameters for evaluating environmental water quality. In this study, unified cation-exchange chromatography with conductimetric detection on an ODS-silica column (TSKgel ODS-100Z) modified with lithium dodecylsulfate was developed to simultaneously determine monovalent cations (Na^+, NH_4^+ and K^+) and H^+/alkalinity. As a result, the simultaneous determination of H^+ as a positive peak and monovalent cations was achieved based on the cation-exchange mechanism. On the other hand, the alkalinity (OH^-/HCO_3^-/CO_3^) was also detected as a negative peak in a vacant peak of the acidity, where alkaline species were neutralized by hydrogen ions in the eluent, while the peaks of monovalent cations and alkalinity were separated. Using the optimized eluent conditions (40mM LiCl/0.1mM Li-DS/0.05mM H_2SO_4 with pH 4.0 ; flow rate, 1.5mL/min), the simultaneous separation of monovalent cation and H^+/alkalinity was achieved in ca. 15 min. Analytical performances tests including a calibration curve, the detection limit, reproducibility and recovery tests were carried out for monovalent cations and acidity/alkalinity under the optimized chromatographic conditions. The present method was practically applied to several acidic and basic environmental water samples (rain, hot spring and river waters) and mineral drinking samples. Since there was a good agreement between the analytical results obtained by the present method and the conventional potentiometry for the acidity and titration method for the alkalinity in these practical samples, the usefulness of the present method was demonstrated experimentally