陰イオンの電量検出イオンクロマトグラフィーにおける炭酸系溶離液バックグラウンドの電気化学的抑制

Electrochemical suppression of carbonate eluent background in coulometric detection-ion chromatography for anion determination.

田中 一彦

中島 良三

黒川 利一

砂原 広志

分析化学

炭酸系溶離液を用いるサプレス型イオンクロマトグラフィー(IC)において, 溶離液中の炭酸によるバックグラウンド(BG)の増大に起因するウォーターディップの除去を目的として, pH4.4における強酸からの水素イオンとp-ペンゾキノンの聞の定電位電解反応を利用した強酸の陰イオンに対して選択検出が可能な電量検出イオンクロマトグラフィーを開発した. 本検出法は, 分析対象となる陰イオンの酸の強さと, 溶離液中の炭酸の強さに大きな差があることに着目して, 炭酸からの水素イオンがほとんど解離していないpH, すなわち, pH4.4における定電位電解反応を利用したもので, 強酸の陰イオンだけが選択的に検出できる. 本法により, 炭酸による溶離液BGは低減し, ウォーターディップは除去できた. 本法は, 富栄養化成分の処理における工程水, すなわち, 生物学的脱窒素及び晶析脱リン処理工程水中の硝酸及びリン酸イオンの定量に良好に応用できた.

The suppressed ion chromatography of anions for the electrochemical suppression of water-dip caused by H+ from carbonic acid in the eluent was investigated with coulometric detector, and applied to the determination of NO3- in biological denitrification process water and PO43- in crystalization process water for phosphorus removal. The detection principle is based on the electrochemical reaction of the H+ of acid eluted from the suppressor column (H+-form) with p-benzoquinone at a constant applied potential. In the chromatograms of anions such as Cl-, NO3-, SO42- and PO43- obtained by the electrochemical reaction at pH 7 under the applied potential of 0.47 V vs. Ag-AgI, although a good chromatogram was obtained, the water-dip was observed due to the H+ from carbonic acid eluent. At pH 4.4, the dissociation of carbonic acid is only 1%, whereas that of the strong acid is almost complete. Therefore, the electrochemical reaction at pH 4.4 under the applied potential of 0.62 V was used to detect the strong acid only. By the proposed method, the water-dip could be removed, and reproducible chromatograms of anions were. obtained (R.S.D. =2.4%). The linear calibration curves were obtained in the concentration range of 10 to 100 ppm for each anion. The detection limits(S/N=2) were 0.03 ppm for Cl-, 0.07 ppm for NO3-, 0.11 ppm for PO43- and 0.10 ppm for SO42- using the injection volume of 0.5 ml. The method was applied to the determination of NO3- and PO43- in several actual samples with satisfactory results.

suppressed anion chromatography

coulometric detector

carbonate/bicarbonte eluent

electrochemical eluent suppression

determination of strong acid anions in denitrification and dephosphorus process waters

化学 [ 430 ]

日本語

日本分析化学会

[ISSN] 0525-1931

[NCID] AN00222633