A flexible method of carbonate determination using an automatic gas analyzer equipped with an FTIR photoacoustic measurement chamber

A Fourier transform infrared spectrometer was employed to determine automat ically the total inorganic carbonate (nc) in solids and waters, based on ac tive photoacoustic absorption of infrared light by carbon dioxide. A 2.0 l reactor, connected to the spectrometer, is immersed in water-bath at 20 deg rees C, After purging with pure N-2, 5 mi of 0.5 mol l(-1) HClO4 are inject ed into 50 mi of solid suspension or solution with continuous stirring. The specific absorption of infrared light by the CO2 evolved induces correspon ding fluctuations of temperature and pressure in a measurement chamber. Acc ordingly, photoacoustic signals, with frequencies dependent on the absorbed wavelengths, are generated and measured by the chamber microphones in the form of an absorption spectrum and concentration. For solids, the method ex hibits a linear response up to 120 mp of CaCO3 with a detection limit of 0. 02 mg; in the case of waters, these figures of merit are 36.4 mmol l(-1) an d 3 mu mol l(-1) NaHCO3, respectively. Since proton consumption by TIC in c lay minerals may commonly influence the evaluation of surface acid-base pro perties, the methodology was applied to determine TIC in three natural illi te samples of different origins. In addition, some potential interferences and modifications of this method are discussed.