LOW TEMPERATURE ANALYTICAL CLOUD POINT EXTRACTION. 1: PROTOLYTIC PROPERTIES OF ACIDIC EXTRACTION INITIATORS IN ORGANIZED MEDIA

Abstract

Cloud point extraction is a powerful tool for the analytical preconcentration of trace amounts of analytes. The standard cloud point extraction procedure requires prolonged heating of the solution, which is not always appropriate in the case of thermally unstable analytes or analytical forms and significantly limits the capabilities of the method. One of the ways to modify cloud point extraction is to find approaches to intensifying the process of analytical concentration. The main disadvantage of cloud point extraction is the need for thermal, ultrasonic, infrared or any other initiation of the formation of the surfactant-rich phase. The difficulty lies in the fact that such influence on the system is not always appropriate and possible, and can also negatively affect the formation of the target analytical form. The purpose of this work is to search for new initiators of cloud point extraction and justify the possibility of their analytical use. In the current paper, the ionization constants (pKa) of some cloud point extraction initiators such as aromatic carboxylic acids (benzoic, 4-chlorobenzoic, 3-nitrobenzoic, 2,4-dihydroxybenzoic, o-, m-, p-toluic and salicylic acids) in water and Triton X-100 micellar solutions at various concentrations of surfactant in the studied systems have been determined by the potentiometric titration method. It was found that the values of pKa of aromatic carboxylic acids (benzoic, 4-chlorobenzoic, 3-nitrobenzoic, 2,4-dihydroxybenzoic, o-, m-, p-toluic and salicylic acids) in water and Triton X‑100 micellar solutions naturally increase with increasing concentration of surfactant in the system. It is shown that the nature and the physico-chemical properties of the environment influence the nature and degree of change in the acid-base properties of the studied aromatic carboxylic acids (benzoic, 4-chlorobenzoic, 3-nitrobenzoic, 2,4-dihydroxybenzoic, o-, m-, p-toluic and salicylic acids). Criteria for the selection of cloud point extraction initiators are proposed, which allow analytical concentration to be carried out at room temperature.