Moisture Analysis Methods – From Laboratory to Process
Regina Kappes, Christian Grimm, Jochen Scholz
Moisture is not only a constituent of many products. It also influences, inter alia, their stability, shelf life and processability. It is precisely for this reason that in the pharmaceutical industry, the moisture of many products is monitored and controlled during production and in inventory to ensure that patients receive perfectly safe medications. This calls for fast and precise measurement of moisture, not just of random samples, but increasingly the entire production process of materials. This trend toward online testing is also substantially driven by the PAT guidelines (Process Analytical Technologies) issued by the FDA. This article describes state-of the-art direct methods for moisture analysis, which will remain important reference methods, and innovative indirect methods for moisture measurement based on microwave resonance and near-infrared (NIR) spectroscopy. For analysis by the microwave resonance method, the sample is exposed to a weak microwave field, which is altered by the sample. This change is used to determine the sample’s moisture. In the method using NIR spectroscopy, samples are irradiated with near infrared light. Samples absorb a part of this light as a function of their composition. The part of NIR light not absorbed by a sample yields information about its composition. Mathematical-statistical evaluations are used to unlock this information on moisture by analyzing the sample’s response to NIR irradiation. Based on various indirect and direct methods, an entire spectrum of instruments custom-tailored to the specific requirements of moisture analysis is currently available for both laboratory and online process applications.
pharmind 2010, Nr. 7, Seite 1231