Knudsen vapor pressure measurements on pure materials and solutions dispersed in porous media: molded nitroglycerin tablets.
The gravimetric Knudsen method for vapor pressure measurement may be subject to serious systematic errors when the sample: (a) consists of the volatile component dispersed in an inert porous matrix and/or (b) contains a dissolved polymeric solute. Vaporization of water present as an impurity in the matrix may result in an appreciable "background" mass loss, and "nonequilibrium effects" may be present; i.e., The vapor of interest may be unable to escape from the sample rapidly enough to maintain the equilibrium vapor pressure in the Knudsen cell. Methods for eliminating the interference due to background effects are described, and a theoretical analysis of nonequilibrium effects is presented. The essential validity of the theories for nonequilibrium effects and the effectiveness of the methods for circumventing background effects were verified by experimental studies with molded nitroglycerin tablets. With nitroglycerin tablets, accurate Knudsen vapor pressure data may be obtained using the modified procedures and data analysis presented in this report.
D055598:Chemical Phenomena; D002626:Chemistry, Pharmaceutical; D002627:Chemistry, Physical; D003720:Densitometry; D004058:Diffusion; D008365:Manometry; D008433:Mathematics; D005996:Nitroglycerin; D013607:Tablets; D014835:Volatilization
D013607:Tablets; D005996:Nitroglycerin