Application of Mid- and Near-Infrared Spectroscopy for the Control and Chemical Evaluation of Brine Solutions and Traditional Sea Salts

Abstract

Mid- and near-infrared spectroscopy methodologies were explored for the analysis of brine solutions and traditional sea salt samples. Brine solutions from different salt pans, corresponding to different stages of sodium chloride crystallisation, were collected. A total of 61 dried and non-dried traditional sea salts were also analysed. Partial least squares regression with leave-one-out cross-validation strategy was applied for the calibration of inorganic constituents Ca²⁺, Mg²⁺ and K⁺, alkalinity as HCO ⁻₃ , SO ²⁻₄ , NO ⁻₂ and NO ⁻₃ and phosphate in brine solutions. Promising results were obtained with the near-infrared (NIR) methodology for brine solutions with coefficients of determination R ² > 0.90 for Mg⁺², K⁺, HCO ⁻₃ and SO ²⁻₄ . Using mid-infrared, the calibration for H₂PO ⁻₄ was R ² = 0.85. In relation to the sea salt samples, the strategy adopted was the re-sampling based cross-validation using different spectral pre-processing treatments. In this case, the calibrations using the two IR methodologies fell bellow acceptable levels for the techniques; however, by comparing the R ² coefficient, the results were slightly better when using the NIR spectra of dried sea samples. In general, these results open a new possibility for the IR applications and also bring an opportunity for continuing with the NIR characterization for dried sea salt samples.