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A level of water that is too high could lead to a reduced shelf life, which could affect patient safety. This raises the question of how to measure water level. There are two established methods: loss on drying (LOD) and Karl Fisher titration (KF). In the pharmaceutical industry, they are often seen as equivalent; but they are not.
LOD is a gravimetric method. Weight loss after heating is judged as loss of water. But LOD cannot distinguish weight loss due to water, versus weight loss due to other compounds such as volatile organics (e.g., oligomers, antioxidants, compounds formed resultant from heating). KF, on the other hand, is a chemical method. It is specific to water, and therefore more accurate. KF is based on a redox reaction that involves stoichiometrically equivalent amounts of iodine and water – end point is measured through volumetric or coulometric means. At West, KF is used for the residual water content information provided for Westar® RU lyophilization stoppers.
Many properties of packaging components/systems and delivery devices can be measured by multiple methods. The key is to select the right methods. In this regard, West’s Analytical Lab Services is well equipped, having the staff, expertise, and facility to not only design studies that support customer needs, but to execute them the right way. For more on how West can help, contact an Account Manager or Technical Customer Support (TCS) representative.
Westar® is a registered trademark of West Pharmaceutical Services, Inc., in the United States and other jurisdictions.