Quantification of hydrofluoric acid species by chemical-modeling regression of near-infrared spectra

Near-infrared spectroscopy in the wavelength region 800-1100 nm has been applied to the measurement of aqueous solutions of hydrofluoric acid over the concentration range 0.01-2.65 M and the pH range 2-13, The analysis is based on the detection of subtle perturbations of the water spectrum which result from the presence of the acid and other species in solution. Spectral characterization of the hydrofluoric acid system was performed using a spectrophotometric titration and multivariate model-based regression, Excellent agreement was observed between the spectra and a simple equilibrium model describing the acid's dissociation, Five species, including hydrofluoric acid, fluoride, bifluoride, hydronium, and hydroxide ions, were quantitated with estimation errors below 10 mM using this procedure, In addition, the species' spectral profiles were recovered, and optimum estimates of the system's equilibrium constants were determined.