INVESTIGATION OF COMPLEX EQUILIBRIA IN SOLUTIONS OF ρ - AMINOHIPPURIC ACID AND TIN (II) ION IN PERCHLORATE MEDIUM Drina Jankovic, Divna Djokic The Vinca Institute of Nuclear Sciences, Laboratory for Radioisotopes Ρ Ο Box 522, 11001 Belgrade, Serbia and Montenegro E-mail: drinaj@vin. bg. ac.yu CONTENTS: Summary 87 Introduction 88 Experimental 89 HPLC analysis 89 Spectrophotometric measurements 89 Potentiometrie titrations 90 Results and discussion 91 HPLC analysis 91 Spectrophotometric measurements 91 Potentiometrie titrations 95 The dissociation constants of PAH 95 Complexation of Sn (II) with p-aminohippuric acid 101 References 104 SUMMARY The complex equilibrium in tin (Il)-p-aminohippuric acid (PAH) solutions in Perchlorate medium was investigated. The interaction between Sn (Il)-ion and PAH was studied with the purpose to establish whether PAH could form complex with Sn (Il)-ion during the labeling with technetium- 99m. HPLC, spectrophotometric and pH-metric methods were used. Dissociation constants of PAH, thermodynamic parameters of PAH dissociation, as well as stability constant of tin (II)-PAH were determined. 87