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.