USE IN PHARMACEUTICAL ANALYSIS OF IONIC ASSOCIATION COMPLEXES FORMED BETWEEN SULPHONEPHTHALEIN DYES AND NITROGEN-CONTAINING COMPOUNDS IN MEDIUM OF ORGANIC SOLVENTS

The review systematizes and discusses data on the new class of reactions based on the formation of ionic association complexes (IAS) between sulfonephtalein dyes (SPD) and basic nitrogen containing organic substances (NOS) taking place in organic solvent. The mechanism of formation of IA, the influence of the nature of organic solvent on the IA formation and the chemical analytical characteristics of the developed methods of analysis are discussed. The reaction mechanism includes the displacement of a tautomeric equilibrium from a colorless lactonic tautomer to an intensively colored yellow quinonoid form, which is due to the formation of IA between the monoanionic form of the SPD and the protonated form of the NOS. The reaction goes better in the environment of polar organic solvents. Chloroform, dichloromethane and acetone are most often used. The formation of IA in most cases occurs very quickly. A large concentration of SPD about 0.01 - 0.1% is required to completely displace equilibrium towards IA. The molar absoprtivity coefficients are high and reach (30-40)x10(3) mol(-1)l cm(-1). The main advantages of new analytical forms are simplicity, speed, lack of complex and lengthy stage of the separation, the possibility of automation. IAs formed between SPD and NOS in organic solvent are attractive and promising forms for use in pharmaceutical analysis.