Synthesis and characterization of 2-(3,5-Dichloro-2-pyridylazo)-5-dimethylaminophenol as a reagent for determination of lanthanum

2-(3,5-Dichloro-2-pyridylazo)-5-dimethylaminophenol (3,5-diCIDMPAP) has been synthesized and its spectral properties, acid—base equilibria, physical constants, and solubility and stability are presented. This reagent is highly promising for the determination of lanthanides. The influence of Triton X-100 on the dissociation constant has been investigated and the association constant between the reagent and the surfactant determined. Analytical data for the 3,5-diCIDMPAP complexes with La(III), Eu(III), Gd(III), Er(III) and Yb(III) are given, La(III) in synthetic samples has been determined with 3,5-diCIDMPAP.