Alizarin complexone–lanthanide(III)–fluoride system: Revised speciation and the origin of the analytical signal

摘要: Abstract Potentiometric titrations of alizarin complexone (ALC) in the presence La(III), Eu(III) and Y(III) 50% vol. DMSO reveal formation mostly binuclear complexes with monoprotonated (LH) completely deprotonated (L) forms ligand type M2L2H2, M2L2H M2L2. Only for La(III) a single mononuclear complex LaLH is observed acidic media. Titrations same mixtures added fluoride show that Y(III), ternary without shifting distribution profile differently protonated bound ALC, but strong shift favor occurs, which explains appearance blue colored species medium giving rise to analytical signal employed quantitative determination fluoride. Detailed analysis spectral properties La(III)–ALC–fluoride system on basis established diagrams demonstrate following factors be involved: (1) fluoride-induced conversion La2L2HF around pH 3; (2) anomalously high affinity La(III)–ALC (3) some sort mutual effect ALC ligands complexes, probably involving change metal coordination number, leading enhanced absorptivity as compared La2L2H.