Absorption spectra and index of refraction of aminophenol compounds are obtained using Terahertz time-domain
spectroscopy (THz-TDS) in the frequency range between 0.3 and 2.0 THz at room temperature. Quantum chemical
calculations are performed to better understand the origin of the absorption features observed in experiments. Different
weight ratios of isomeric mixtures are analyzed by THZ-TDS with the help of linear regression technology. It is
concluded that THZ-TDS is able to identify the components and their relative percentage in isomeric mixtures.
Terahertz spectroscopy has tremendous potential for applications to evaluate the quality of the drugs including the TCM.
In this paper, the Terahertz Time-Domain Spectroscopy investigated two active ingredients: Andrographolide and
Dehydroandrographoline, isolated from Andrographis paniculata (Burm. f.) Nees. We also measured the mixtures of two
active ingredients at the different ratio and the quantitative analysis is also applied to determine the contents of
compound. The Terahertz spectroscopy is a potential and promising technique in identifying the components, evaluating
the drugs sanitation and inspecting the quality of medicine including TCM.