Chemiluminescent reactions of heteropoly acids and their complexes with cationic surfactants in aqueous solutions and on the cellulose surface

Abstract

The properties of heteropoly acids and of their complexes with cationic surfactants at the trace level have been studied by ESR spectroscopy, UV-VIS spectrophotometry, NMR and FTIR spectroscopy, by the method of chemiluminescence analysis applied in aqueous solutions and on the cellulose surface. For elucidation of the mechanism of chemiluminescence reactions of heteropoly acids with luminol kinetic methods, diffuse reflectance spectroscopy and liquid chromatography have been applied. For the first time one-electron reduction of heteropoly acids by luminol was confirmed by registration of diffuse reflectance spectra of reduced heteropoly acids on cellulose surface. It has been suggested that the mechanism of heteropoly acids immobilization on cellulose includes combination of Coulomb and hydrophobic interactions. A scheme of heteropoly acids immobilization on the surface was proposed based on ion exchange processes on cellulose or diethylaminoethyl cellulose surface. It has been shown that ionic associates heteropoly acid – cationic surfactant react with an alkaline solution of luminol with light emission similarly to heteropoly acids themselves. For the first time, heterogeneous chemiluminescence, namely, the chemiluminescence of heteropoly acids immobilized on cellulose, with luminol, has been used for examining the composition of ionic associates heteropoly acid - cationic surfactant. By using Bjerrum’s method it has been found that in strongly acidic media (at pH 1.0) vanadomolybdophosphoric acid forms with cationic surfactant, namely, with dodecylpyridinium bromide, not tetra-substituted but triply substituted ionic associate. This result can be explained by the fact that the fourth proton in H₄PVMo₁₁O₄₀ is weakly dissociated; it is more strongly bound to heteropoly anion and is localized on the oxygen atom of the Mo–O–Mo angular bond. Ionic associates of heteropoly acids were used as analytical forms for highly sensitive chemiluminescence determination of P, As, Si, Ge in waters of different types. Detection limits for P, As, Si, Ge are 0.02–0.07 µg/L. Due to the high sensitivity of the method, phosphorus was successfully determined in surface water and ultrapure water, arsenic – in river and mineral water, silicon – in ultrapure water and vapor condensate of electric power stations, germanium – in water of electronic industry.