Vapour phase Fourier transform infrared spectrometric determination of carbonate in sediments

Abstract

A rapid, sensitive and direct procedure for the determination of carbonate in sediments based on vapour-generation Fourier transform infrared spectrometry is described. A 1 ml volume of hydrochloric acid (0.25 M) was injected into a vessel, heated at 40 °C, containing 10 mg of sediment. The CO₂ evolved under these conditions was swept by a stream of nitrogen to an infrared gas cell. The flow injection (FI) recordings were registered as a function of time and the areas of the FI recording obtained in the wavenumber range 2500–2150 cm^–1 were measured and interpolated in a calibration equation obtained from known amounts of CaCO₃ treated in the same way as the samples. The method provided a limit of detection of 0.2 mg of CaCO₃, a sampling frequency of 20 h^–1 and an RSD of 0.7% for three independent analyses of 20 mg of sediment. Results obtained for a series of natural sediment samples compared well with those obtained using a back-titrimetric reference method.