Desiccants are used to remove moisture from air in containers in order to protect drug products, particularly solid oral dosage forms. They are supplied in a number of different packaging materials including cotton, Kraft paper, rayon and polyester cloth bags, perforated plastic, polymer films, polymer housings or Tyvek®. The most common types of commercial desiccants are bentonite, calcium chloride, calcium oxide, molecular sieves, and silica gel. Like other components that comprise a package system, desiccants are subject to strict qualification testing as outlined and directed in the USP <670> General Chapter especially as it relates to their Adsorption Capacity.

For those systems where desiccants are incorporated directly into the wall or cap of packaging containers or bound by a carrier material, unincorporated desiccant should be used in the performance of the testing outlined. For desiccants that are loaded with a predetermined moisture content, testing should be performed before the moisture has been loaded or after the desiccant has been regenerated.

Moisture adsorption capacity requires temperature-humidity chambers capable of controlled humidity at 40% ± 5% RH and 80% ± 5% RH at 25 ± 2°. The desiccant sample is stored in the chamber and weight gain is measured over time until it reaches equilibrium defined as two successive consecutive weighings that do not differ by more than 3 mg/g of substance taken with the second weighing following an additional 3 ± 1 h of storage at the required temperature and humidity conditions. Adsorption capacity is calculated as percentage weight gained over the initial sample weight.

The acceptance criteria vary for the type of desiccant being tested and in some cases multiple desiccant types may be mixed to form one sample type. CS Analytical maintains the necessary instrumentation and the team has experience with adsorption capacity testing as part of our routine container and package testing service platform.