This article presents a description of the method of obtaining a new acidic dye compound and sorption-spectroscopic detection of the metal ion in the immobilized fiber through the ligand complex of Pb (II) ion from heavy metals with an azo acid dye - Amido Black 10B. The properties of the ligand and the new azo complex were analyzed by FT/IR spectroscopy, UV-Vis spectroscopy, and reflection spectroscopy. The structure of the ligand immobilized on the fiber and the newly synthesized lead complex was studied by all the methods of analysis mentioned above. Formation of azo metal complex with Pb (II) was confirmed by UV-Vis spectrum. The proportion of the complex immobilized on this fiber in different pH environments and by spectral analysis was revealed by the method of isomolar series. Mechanisms of immobilization of organic ligands to synthetic polymer fiber, optimal conditions were determined and tested in artificial mixtures.