Thermogravimetry (TG) is specified in the U.S. Pharmacopeia for the compositional analysis of certain drugs. It is specified for use in determining the percentage of volatile substances in drugs such as vincristine sulfate and vinblastine sulfate. TG reveals interactions between a controlled atmosphere and a drug and between an active substance and excipients. TG is used in the compositional analysis of injectable biological products in various ways. For pneumococcal, Haemophilus b, and meningococcal bulk polysaccharides that are used in vaccine production, TG is used to determine the moisture content (approximately 5 to 25 percent) so that the content of protein, nucleic acid, phosphorus, and other constituents may be accurately determined on a dry weight basis to demonstrate that a sample meets the specifications for the product. TG is also used to determine residual moisture in freeze-dried final container biological products such as Blood Grouping Sera and Antibody to Hepatitis B Surface Antigen. TG is used to confirm or supplement information obtained from Karl Fischer or gravimetric (loss on drying) moisture analysis techniques. TG has been combined with mass spectrometry to verify moisture data for group Y meningococcal poly-saccharide and freeze-dried antibody to hepatitis B surface antigen and to identify an impurity in a Haemophilus b polysaccharide.
Exterior water can penetrate a building and move in either continuous or discontinuous flow. In the case of continuous flow, from point of entry to point of observation, surfaces of construction materials are wetted and may provide a path of adequate conductivity to produce a detectable alternating electric field when a voltage is applied. Where this is the case, a suitable a-c ource and detector can be used to determine the source of water entry. For cases where water flow is discontinuous, detection of vapor from water mixed with organic solvent can assist in tracing water movement and source of origin. Commercial equipment is available to measure, non-destructively, moisture behind and within non-conducting substrates such as wood and exterior foam panels. Using these methods one can often unambiguously locate the source of a water leak.
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