4-(2-ピリジルアゾ)-レゾルシン・第4級アンモニウム塩・ポリアミノカルボン酸系を利用する極微量金属の抽出吸光光度法

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The chelates of 4-(2-pyridylazo)-resorcin with iron (II), cobalt, nickel and vanadium (V) react with quaternary ammonium salts (tetradecyl-dimethylbenzyl ammonium chloride) to form red association complexes soluble in chloroform in the presence of a large excess of polyaminocarboxylic acid (PC) such as EDTA (for Ni2+, Co2+ and Fe2+) and CDTA (for V5+). The EDTA and CDTA not only act as masking agents for interfering metals, but also increase the molar absorption coefficient, ε, of the complexes in the organic phase. The numerical value of ε varies as a function of PC concentration at [PC] <10-3M (for example, εNi2+ has a maximum value of 1.2×105 at [PC]=5×10-4M, pH=9.3, 505 mμ), however, the ε valule is constant at [PC]>10-3M (εNi2+=7.65×104 at 505 mμ; pH=9.3, εCo2+=5.9×104 at 520 mμ; pH=8.3, εFe2+=4.0×104 at 522 mμ; pH=10, εV5+=4.3×104 at 560 mμ; pH=6.8). Based on these results, a highly selective and sensitive method for the determination of Ni2+, Co2+, Fe2+ and V5+ has been proposed. The mechanism of the increase in ε by polyaminocarboxylate is also discussed.
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