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Small Variation of Active Pharmaceutical Ingredient Concentration Can Be Observed with THz Frequency Domain Spectroscopy

Terahertz frequency domain spectroscopy (THzFDS) has been employed to study the result of variation of active pharmaceutical ingredients (API) on the effective refractive index of pharmaceutical tablets. A quasi-optical set-up with four off-axis parabolic mirrors was used to measure the effective refractive index of tablets in the frequency range of 500-750 GHz. It was observed that a small variation in API concentration can be detected using accurate measurements of the complex transmission coefficients. As a results, THz-FDS reveals to be an effective technique in monitoring the physical properties of pharmaceutical tablets.