Terahertz spectroscopy of citrate Salts: Effects of crystalline state and crystallization water.

Citrate salts are widely used as food additives and medicines for health and treatment. Accurate and fast detection of citrate salts is most important in food industry and medicine health. In this work, terahertz (THz) time-domain spectroscopy was used to detect and analyze different citrate salts and differentiate their crystalline hydrates. Effects of the crystalline state, the crystallization water and the metal cation on the THz spectra of citrate salts were investigated. Results indicate the crystalline states of the citrate salt samples strongly influence their THz featuring absorption peaks and citrate salts with crystallization water have larger absorption coefficients at the same frequency and higher possibility of existing featuring absorption peaks in comparison with citrate salts without crystallization water. Size of the metal cation also influences the THz absorption peak of the citrate salt and a small cation radius results in a large absorption peak frequency. This work illustrates the terahertz spectroscopy can be well used as a new technique to detect the citrate salts and differentiate their crystalline hydrates.