Characterizations of the Calamine tablets by terahertz time-domain spectroscopy

Abstract Terahertz time-domain spectroscopy (THz-TDS) is an attractive technique that is capable of non-destructive penetrating and probing pharmaceutical tablets conveniently. It can provide sufficient optical information of crystalline and polymorphic pharmaceuticals with high signal-to-noise ratio (SNR). These merits make the application of THz-TDS within pharmaceutical industry increase rapidly. Meanwhile, the advancements of the in-line monitoring accuracy and dependence of THz-TDS are highly urgent because of the rigorous pharmaceutical quality control. There, it is the first time to characterize the optical constants of Calamine tablets using THz-TDS. The experimental results prove that THz-TDS can be employed to classify Calamine tablets with different masses. In addition, the issue of existing echo signal has been resolved with enhanced SNR by a novel wedge-tablet design within a minor wedge angle. Furthermore, the relationship between the particle sizes composed the Calamine tablets and the scattering absorption obtained from terahertz spectra is revealed. This research highlights the character of THz-TDS in distinguishing the Calamine tablets composed with different configurations, as well as further deepening the interpretation of in-line monitoring in the pharmaceutic industry.