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

Abstract

A Fourier transform infrared spectrometer was employed to determine automatically the total inorganic carbonate (TIC) in solids and waters, based on active photoacoustic absorption of infrared light by carbon dioxide. A 2.0 l reactor, connected to the spectrometer, is immersed in water-bath at 20 °C. After purging with pure N 2 , 5 ml of 0.5 mol l 21 HClO 4 are injected into 50 ml of solid suspension or solution with continuous stirring. The specific absorption of infrared light by the CO 2 evolved induces corresponding fluctuations of temperature and pressure in a measurement chamber. Accordingly, 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 exhibits a linear response up to 120 mg of CaCO 3 with a detection limit of 0.02 mg; in the case of waters, these figures of merit are 36.4 mmol l 21 and 3 µmol l 21 NaHCO 3 , respectively. Since proton consumption by TIC in clay minerals may commonly influence the evaluation of surface acid-base properties, the methodology was applied to determine TIC in three natural illite samples of different origins. In addition, some potential interferences and modifications of this method are discussed. Experimental ReagentsAll chemicals used in the experiments were of analyticalreagent grade or better. A 0.04 mol l 21 stock standard solution

Determination of carbonate in marine solid samples by FTIR-ATR spectroscopy

“…So, for the instrumental calibration, the optimal resolution is 4 cm 21 because it solves the problem of non-linearity observed in previous FTIR-ATR determination of carbonate in soils, 4,6 covering almost the whole natural range of IC in environmental solid samples.…”

“…3 The IC content of waters and solids has been measured by the photoacoustic absorption of IR radiation. 4 High resolution FTIR spectroscopy has been used to measure the 13 C + 12 C ratio in CO 2 evolved from soils and rocks. 5 These methods which require a preliminary acid or combustion step to convert carbonate into CO 2 , are very sensitive and reproducible.…”

“…A method without the conversion step carbonate into CO 2 , based on attenuated total reflectance (ATR) IR measurements has been proposed to measure carbonate in soils 6 but some limitations such as non-linear calibration and poor reproducibility still remain. 4 In this paper we perform a re-examination of the FTIR-ATR method to measure IC content in different environmental samples such as marine sediments and corals. With a careful optimisation of the experimental procedures including drying process, deposition of the sample on the ATR crystal and spectral resolution, the problems related to poor reproducibility and non-linear calibration can be solved.…”

ATR-FTIR Spectroscopy, a New Non-Destructive Approach for the Quantitative Determination of Biogenic Silica in Marine Sediments

“…The band at 800 cm −1 corresponds to an inter-tetrahedral Si–O–Si bending vibration mode, and the band near 945 cm −1 to an Si–OH vibration mode [37]. Previous studies have shown that the absorbance centered around 1640 cm −1 and between 3000 and 3750 cm −1 can be attributed to hydroxyl vibrations because hydroxyl ions are major constituents of clay minerals, opal, and organic compounds present in marine sediments [38]. However, these bands are not specific for silica, their intensity is generally low (about one-tenth of the main band); moreover, they are overlapped with the residual absorption bands of H 2 O.…”

Facile synthesis of an optical sensor for CO32−and HCO3−detection

“…In view of widespread occurrence of carbonate and bicarbonates in physiological, industrial and environmental samples, there exists a necessity of a durable, accurate and rapid sensor for biomedical applications, clinical and environmental analysis with potential for real sample investigation without interference from endogenous substrates [20][21][22][23][24][25][26]. A number of analytical methods have been developed for carbonate detection including Fourier transform infrared (FT-IR) spectroscopy [27], passive acoustic emission [28,29], gas chromatography [30], pH-ion-sensitive field-effect transistor as a sensitive element [31,32], ionselective electrodes [19,[33][34][35] and chromoionophore based optodes [36]. Alongside, the development of luminescent signalling systems utilising organic chromophores is an active area of research in photochemistry to establish fluorescent chemosensors which can be applicable to industry, diagnostic and various kinds of environmental monitoring.…”