Highly selective spectrophotometric determination of ultramicro amounts of copper with cationic porphyrins in the presence of a reducing agent

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  • ISHII Hajime
    Chemical Research Institute of Non-Aqueous Solutions, Tohoku University
  • KOH Hidemasa
    Chemical Research Institute of Non-Aqueous Solutions, Tohoku University

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  • 還元剤の存在下で陽イオン性ポルフィリンを用いる超微量銅の選択的吸光光度定量
  • カンゲンザイ ノ ソンザイカ デ ヨウイオンセイ ポルフィリン オ モチイル
  • ポルフィジンの分析化学的応用に関する研究(VI)

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Abstract

It has been found that the complexation of α, β, γ, δ-tetrakis (1-methy1-3-pyridyl) porphine [T (3-MPy)P] or α, β, γ, δ-tetrakis (1-methyl-4-pyridyl) porphine [T(4-MPy)P] with copper(II) is accelerated remarkably by adding a small amount of a reducing agent such as hydroxylamine, ascorbic acid or sulfite, and is completed almost instantaneously even at room temperature. On the basis of this finding, two highly selective spectrophotometric methods have been developed and proposed for the determination of copper at ppb level. In the method using T(3-MPy)P, the calibration curve obeyed Beer's law up to at least 140 ppb of copper and the sensitivity for 0.001 absorbance was 0.179ng Cu/cm2. In the method using T(4-MPy)P, the calibration curve was linear up to 190 ppb and the sensitivity was 0.258 ng Cu/cm2. The procedure of the T(3-MPy)-P method is as follows; To a 25-ml volumetric flask, a sample solution containing less than 3.5μg of copper, 1 ml of 0.5% hydroxylamine hydrochloride solution, 1 ml of 1 M acetate buffer solution(pH 5) and 1 ml of 6×10-5 M T(3-MPy)P solution are added. After standing for about 2 min, 4 ml of sulfuric acid(1+1) is added and then the solution is diluted to the mark with water. The absorbance of the solution is measured at 434 nm against water. The method was applied to the determination of copper in analytical reagents, cement and steel with good accuracy and reproducibility.

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 28 (8), 473-477, 1979

    The Japan Society for Analytical Chemistry

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