Quantitative analysis of binary mixtures using Molecular Absorption Spectroscopy

Abstract

Molecular absorption in the spectral region between 160 and 780 nm is caused by electronic arousal of absorbent species. In wavelengths below 400 nm, incident radiation energy is sufficient to break chemical bonds, while in the infrared region (over 780 nm), mainly molecular vibrations are observed. Since chemical species that absorb in the UV-vis region of the electromagnetic spectrum have wide absorption bands, simultaneous determinations of multiple species are more complicated, given the difficulty in finding appropriate wavelengths that allow the direct measurement of the individual concentration of each component in the mixture. Considering the simplest situation, where the sample consists of only two absorbent species in solution, the most direct and efficient procedures that can be used to solve this problem are the algebraic method, the double wavelength spectroscopy method and the standard addition method at point H (HPSAM). Of these, the latter seems to be more efficient as it allows you to eliminate or reduce systematic errors. Experimental procedures and calculations associated with these methods will be presented in this work, taking as an example the simultaneous determination of the concentrations of two distinct ions in an acidic aqueous solution.