**4.4 Deliquescency vs hygroscopicity**

Hygroscopicity can be defined as the capacity of a compound to absorb atmospheric moisture. Amount of moisture absorbed depends on atmospheric conditions and surface area. Deliquescent substance absorbs moisture to a greater extent and liquefies itself. The main reason behind study of this property is because changes in the moisture level can influence chemical stability, flowability, and compressibility to a greater extent.

In European pharmacopeia, hygroscopicity is described by four different classes after being stored at 25°C at relative humidity of 80% for 24 hours.


For this study, samples under analysis are exposed to range of controlled relative humidity prepared with saturated aqueous salt solutions (**Table 4**). One can link flowability and relative humidity by amount of moisture uptake (**Table 5**).

Moisture level uptake can be monitored by techniques like thermogravimetric analysis (TGA), Karl Fischer titration, and gas chromatography.


**Table 4.**

*Utilization of different salts to give environment with different RH.*


**Table 5.**

*Use of different process to control particle size, shape, and surface area.*
