Discrimination of hydration states of hydrated salts using terahertz time-domain spectroscopy

Abstract

Water-sensitive nature of terahertz radiation has been exploited here to discriminate the hydration states of different hydrated salts, such as Cobalt Chloride Hexahydrate (CoCl2.6H2O), Copper Sulfate Pentahydrate (CuSO4.5H2O), Magnesium Chloride Hexahydrate (MgCl2.6H2O), and Calcium Chloride Dihydrate (CaCl2.2H2O). Hydration states of these salts have been prepared by heating them in an oven at different temperature for specific time on the basis of thermo-gravimetric analysis. The prepared samples were analyzed using terahertz time-domain spectroscopy (THz-TDS). The variation in absorption coefficient and refractive indices of these hydrated salts in terahertz spectral regime (0.2–1.6 THz) are linked with the change of hydration states, which has been used for their discrimination. The results have been validated with X-ray diffraction analysis. The present work indicates that THz-TDs can be considered a promising technique to fulfill the ever increasing demand of the analysis of these hydrated salts.