DETERMINATION OF PARA-HYDROXYBENZOIC ACID AND ITS ESTERS IN SOLID PHASE OF SORBENT WITH USING OF SENSITIZED LUMINESCENCE OF Tb(III) IN COMPLEX WITH 2,2’-DIPYRIDYL

Abstract

A Tb(III) – 2,2’-dipyridyl complex as a luminescent sensor for determination of p-hydroxybenzoic acid and its esters was proposed. The luminescent properties of the complex with phydroxybenzoic acid and p-hydroxybenzoates in a solid layer of sorbent were studied. The absorption spectra, luminescence spectra, excitation spectra, the triplet energy levels of ligands were analysed. An energy transfer from the triplet state level of the ligands to the resonance level of the Tb(III) ion was observed resulting in more intense luminescence. The optimal conditions of complex formation (the optimal concentration of terbium(III) chloride, dipyridyl, p-hydroxybenzoic acid and its methyl-, propyl- and butyl esters) were selected. The maximal luminescence intensity was occurred at 1·10–3 mol/L Tb(III) in neutral solutions at pН 6,5 – 7,5. The maximal luminescence intensity of Tb(III) – 2,2’-dipyridyl – p-hydroxybenzoic acid complex was observed at 1,5 ∙ 10–2 % dipyridyl and at 2·10–4 mol/L p-hydroxybenzoates. The Tb(III) sensitized luminescence method for determination of p-hydroxybenzoic acid in model solutions and its methyl ester in makeup removers has been proposed. The limit of detection is 1,0 μ/ml for p-hydroxybenzoic acid. The proposed method is simple and does not require heavy processing algorithm so it could be applied on low cost control system.