Quantitative analysis of aragonite-group carbonates synthetic mixtures using attenuated total reflection Fourier transform infrared

Aragonite is the second most abundant calcium carbonate (CaCO 3 ) mineral in the natural environment. Aragonite usually incorporates other trace elements such as strontium (Sr) and barium (Ba) or co-precipitates with other minerals such as strontianite (SrCO 3 ) and witherite (BaCO 3 ). In this work, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy proved to be a promising method for analysing aragonite-group carbonates. The technique is simple, rapid, and accurate and requires little to no sample preparation, making it a practical alternative to X-ray diffraction (XRD) for rapid qualitative and quantitative analysis of aragonite sediments as important indicators of precipitation conditions. To reduce instrumental and methodological variations, the quantitative analysis relied on absorbance ratios at characteristic wavenumbers instead of absolute absorbance values. Linear calibration relationships between weight percentages and absorbance ratios were obtained over a wide compositional range, with high coefficients of determination ( R 2 ). As examples, the following equations were obtained for quantitative determination of (SrCO 3 ) and (BaCO 3 ): weight % of SrCO 3 in aragonite mixture = -425.81x+433.2 with R 2 =0.9932, where x is absorbance at 1474.6 cm −1 / absorbance at 855.1 cm −1 , while the weight % of witherite in aragonite mixture = -138.7x+200.09 with R 2 =0.9783, where x is absorbance at 853.7 cm −1 / absorbance at 856.5 cm −1 . It should be noted that this study only deals with pure physical mixtures of aragonite group minerals and not with solid solutions. The new method should be calibrated for natural samples.