Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 853763, 10 pages http://dx.doi.org/10.1155/2013/853763 Research Article Reactions of o,o  -Dihydroxy Azo Dyes with the Third Group M(III) Ions: A Spectroscopic and Electrochemical Study Solomiya Pysarevska, 1 Liliya Dubenska, 1 Ivan Spanik, 2 Jaroslav Kovalyshyn, 3 and Sofia Tvorynska 1 1 Department of Analytical Chemistry, Ivan Franko National University of L’viv, Kyryla i Mephodia Street 6, L’viv 79005, Ukraine 2 Institute of Analytical Chemistry, Slovak University of Technology, Radlinskeho Street 9, Bratislava 81237, Slovakia 3 Department of Physical Chemistry, Ivan Franko National University of L’viv, Kyryla i Mephodia Street 6, L’viv 79005, Ukraine Correspondence should be addressed to Solomiya Pysarevska; pysarevska s@mail.ru Received 26 May 2013; Revised 12 September 2013; Accepted 24 September 2013 Academic Editor: Fernando Garay Copyright © 2013 Solomiya Pysarevska et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te reactions of some metal ions of the third group (M(III)) with azo dyes were studied. Attention was focused on azo dyes with two hydroxy groups in ortho-positions to azo group: eriochrome red B (ERB), eriochrome black T (EBT), eriochrome blue SE (EBSE), calcon (Calc), and kalces (KLC). Te chelation is responsible for interaction of these dyes with Al(III), Sc(III), rare earth elements (REE) ions, Ga(III), and In(III). Te complexes were studied using vis- and IR-spectrometry. One irreversible peak (P1) of complexes reduction was observed on voltammograms for all studied metal ions. Te second peak P2 was observed only for Ga complexes with all investigated azo dyes. Based on the study, the possible mechanism of complexes reduction was proposed. Linear behavior has been found between the reduction peak currents of a set of metal complexes and the concentration of the respective metal cations. Tis can be used for metal ions determination by voltammetric methods. 1. Introduction Azo dyes belong to the one of the largest class of analytical reagents. Teir important feature is electroactivity, which makes them very important reagents for the voltammetric determination of metal ions [1–3], especially nonelectroactive metals. It is known that the electrochemical behaviour of Al(III), Sc(III), Ga(III), and REE(III) is not straightforward [4–8]. Te reduction potentials of these metal ions are more negative than −1.2 V on mercury electrodes. Terefore, direct voltam- metric methods for Al(III), Sc(III), Ga(III), and REE(III) determination are limited by a concurrent reduction of hydrogen ion. Another possibility is indirect analysis based on the formation of complexes of M(III) with reducible organic reagents, such as azo dyes. Te resulting complex produces a discrete reduction peak which is well separated from the peak of free dyes and measured current of complex reduction is sensitive to M(III) concentration. In our previous papers, the complexes of some M(III) ions with ERB, EBT, EBSE, Calc, and KLC were studied [9–12]. Methods developed were utilized for voltammetric determination of REE, In, and Sc in model solutions, alloys, and scintillation materials with the limit of quantitation in range 10 −7 –10 −6 M. Te observed diferent reduction behav- ior of studied complexes leads us to investigate peculiarities of M(III) interaction with azo dyes—ERB, EBT, EBSE, Calc, and KLC. Teir structures are shown in Figure 1. 2. Experimental 2.1. Apparatus. A potentiostat ^J-50-1.1 (Russia) connected to a personal computer was used for electrolysis and cyclic voltammetric measurements. Linear sweep voltammetric measurements were carried out utilizing certifed home- made digital device equipped with personal computer and temperature-controlled three-electrode cell, volume 10 mL.