CHARACTERIZATION OF A SINGLE-SAMPLE BY COMBINING THERMODYNAMIC AND SPECTROSCOPIC INFORMATION IN SPECTRAL-ANALYSIS

We have previously shown that chemical equilibria can be characterized spectroscopically, even when the component spectral responses are unk nown and overlapping, by exploiting appropriate thermodynamic relation s (Kubista, M,; Sjoback, R,; Albinsson, B, Anal, Chem, 1993, 65, 994-9 98), Application of this strategy requires sets of samples that differ in a physical property, such as pH or total concentration, In this wo rk, we show that a similar strategy can be applied to characterize a s ingle sample, Utilizing the van't Hoff relation, which describes the d ependence of the equilibrium constant on temperature, we show that spe ctra recorded at different temperatures can be deconvoluted into contr ibutions from the individual components, To illustrate the approach, w e characterize two monomer/dimer equilibria, thiazole orange in aqueou s solution and benzoic acid in n-heptane, by studying the effect of te mperature on the absorption spectrum, We determine the spectral respon ses of the monomer and dimer species, their concentrations as a functi on of temperature, and the enthalpy change upon dimerization, These ar e the first examples ever where the spectral responses of the componen ts in a single sample are determined without making assumptions about spectral overlap and without reference spectra.