ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2010, Vol. 36, No. 8, pp. 627–630. © Pleiades Publishing, Ltd., 2010. 627 1 INTRODUCTION It is well known that mixed ligand coordination complexes play an important role in biological systems [1]. Hippuric acid (N-benzoylglycine) is an α-amino acid containing acidic COOH, basic NH, and substit- uent benzoyl group. It is thus capable of forming metal chelates. It has a special biological significance, as it is found in the urine of camel. p-Amino hippuric acid (PAH), a derivative of hippuric acid, is a compound useful in the medical tests used in the measurement of renal blood flow. Mixed metal complexes play an important role in various biological systems and in dif- ferent fields of chemistry [2, 3]. Hence, the formation stability and reactivity of these complexes have been an active field of research [4]. Several binary and ter- nary metal complexes of hippuric acid and its deriva- tives have been reported [5, 6]. Its alkali-earth metal salts (calcium and magnesium) have been used as sol- ubilizers in the preparation of aqueous solutions of some sparingly soluble medicinal compounds [7]. The present work [8] describes the ionophoretic technique for the determination of stability constants of the com- plexes formed. A simple electrophoretic tube [9] has been designed, which after standardization yields remarkable results. EXPERIMENTAL Instruments. Electrophoresis equipment from Systronic (Naroda, India) model 604 was used. It has a built in a power supply (AC-DC) that is fed directly to an electrophoretic tube (18 cm long and 0.5 cm bore) with a stopper in the middle, which was fused 1 The article is published in the original. perpendicularly at the ends with short wider tubes of 1.2 cm bore. This tube is kept in a thermostatic water bath at 25°C. The pH measurements were made with a century CP 901 digital pH-meter using a glass elec- trode. Absorbance were measured with SPECTRO- CHEM MK II (PEI) spectrocolorimeter. A SICO constant-temperature water bath has been used to ensure uniform temperature. Chemicals. Fe(III), Cu(II), Ni(II), and Co(II) perchlorate solutions were prepared by precipitating the corresponding carbonates from a solution of chlo- rides (A. R. grade) with a solution of sodium carbon- ate, washing the precipitates thoroughly with boiling water and dissolving in a suitable amount of perchloric acid. The resulting solutions were heated to boiling in a water bath and then filtered. The solutions were stan- dardized and diluted with distilled water as required. AR grade hippuric acid, NaOH, HClO 4 , and a devel- oping reagent for color development were used for specific color development for different metal ions of binary system sets. Electrolytic solutions. For binary systems 15 ml of a solution each containing 1 × 10 –3 M Cu(II)/Ni(II)/Co(II), 0.1 M HClO 4 , and 1 × 10 –2 M hippuric acid was prepared at different pH values (by adding a NaOH solution). In the case of Fe(III), 1 × 10 –4 M Fe(III), 0.1 M HClO 4 , and 1 × 10 –3 M hippuric acid were used. For ternary systems, the study was car- ried out by preparing sets of 15-ml solutions by the progressive addition of secondary ligand NTA from 1 × 10 –6 to 1 × 10 –2 M at fixed pH 7.0 to a mixture of metal ion (having the same concentration as in binary systems), 1 × 10 –2 M hippuric acid, and 0.1 M per- chloric acid. Electrophoretic Studies on Mixed Complexes Metal–Hippuric Acid–Nitrilotriacetate 1 P. Kumar, P. P. Singh, V. K. Nigam, S. Singh, and R. K. P. Singh* Electrochemical Laboratory of Green Synthesis Department of Chemistry, University of Allahabad, Allahabad 211002, India *E-mail: rkp.singh@rediffmail.com Received December 12, 2009 Abstract—In the present communication the ionophoretic technique has been used for the study of Fe(III), Cu(II), Ni(II), and Co(II)–hippuric acid binary and Fe(III), Cu(II), Ni(II), and Co(II)–hippuric acid– NTA ternary complexes (NTA – nitrilotriacetic acid). The stability constants of metal–hippuric acid binary complexes are found to be 10 3.54 , 10 2.95 , 10 2.77 , and 10 2.70 and the stability constants of metal–hippuric acid NTA ternary complexes have been found to be 10 6.16 , 10 6.06 , 10 6.01 , and 10 5.90 for Fe(III), Cu(II), Ni(II), and Co(II) complexes, respectively, at μ = 0.1 M (HClO 4 ) and 25°C. DOI: 10.1134/S1070328410080130