Pharmaceutical Analysis using Terahertz Spectroscopy

TERAHERTZ LIGHT Terahertz (THz=10Hz) radiation represents the last unexplored frontier of the radio wave and light spectrum. The so-called ‘Terahertz Gap’ encompasses frequencies invisible to the naked eye in the range from 100GHz (10Hz) up to roughly 30THz (3x10Hz). The former limit lies just above the microwave region, whereas the latter limit is located adjacent to infrared frequencies; the gap is a fusion between microwaves and infrared light (Figure 1). Conventional microwave sources do not work fast enough (at high enough frequencies) to efficiently produce radiation in the gap, whereas laser diode sources have been limited by thermal effects. However, recently, advances in ultra-fast pulsed laser technology have led to the generation and detection It has long been known that many pharmaceutical solids can exist in more than one crystalline form (1); these different forms or polymorphs have the same chemical formula but different crystalline structures. This can lead to different physicochemical properties and may also impact on the pharmaceutical properties of a compound. For example, different polymorphs may have different rates of dissolution or bioavailability, and the stability of a drug may also be affected (2). Polymorphism is very common among drug compounds and has been observed in 67% of steroids, 40% of sulphonamides and 63% of barbiturates.