3-[(2-アルソノフェニル)アゾ]-4,5-ジヒドロキシ-2,7-ナフタレンジスルホン酸

解説2-(1,8-dihydroxy-3,6-disulfo-2-naphthylazo)phenylarsonic acid disodium salt．C16H11AsN2Na2O11S2(592.29)．ネオトリンともいう．o-アミノアルソン酸をジアゾ化し，クロモトロープ酸にアゾカップリングさせると得られる．"深赤色の粉末．pK1 0.1，pK2 1.2，pK3 2.7，pK4 7.9，pK5 10.5．多くの金属と赤～青紫色の水溶液キレート錯体をつくるので，三ナトリウム塩はキレート滴定の指示薬，比色試薬に用いられる．トリウム(Ⅳ)，ウラン(Ⅵ)，ニオブ(Ⅴ)，タンタル(Ⅴ)，希土類，そのほかの金属イオンの比色定量に用いる．[CAS 520-10-5][CAS 3547-38-4:三ナトリウム塩]森北出版「化学辞典（第2版）

使用The reagent reacts with many metal ions, such as uranium(IV), thorium(IV), zirconium(IV), scandium(III), lanthanum(III), cerium(III), aluminium(III), beryllium( III), titanium(III), niobium(lll), tantalum(III), vanadium(IV), tin(IV), bismuth( III), gallium(III), copper(III), palladium(II), magnesium(II) and calcium(II) to give coloured complexes. It has been used for the photometric determination of the majority of the above-listed metal ions. Though the reagent reacts with such a variety of metal ions, the complex formation reaction may be made selective for individual metal ions by appropriate choice of the reaction conditions, primarily of the pH of the solution. For instance, thorium can be determined with Arsenazo I in the presence of almost all rare earth metals, and similarly zirconium and thorium in the presence of uranium, etc. The stabilities of the metal complexes of Arsenazo I are lower than those of the corresponding complexes of EDTA. It can also therefore be used advantageously as indicator in complexometric determination of some metals (e.g. plutonium, thorium). The analytical sensitivity of the formation of Arsenazo I complexes is comparatively high (0.05-0.1 γ/ml). However, the importance of the reagent is decreasing in analytical practice, in parallel with an increase in significance of the related reagent, Arsenazo III, which gives more stable complexes with higher absorbances, and which is therefore of greater analytical sensitivity.