High-precision absolute (true) density measurements on hygroscopic powders by gas pycnometry: application to determining effects of formulation and process on free volume of lyophilized products.
Kikuchi T, Wang BS, Pikal MJ. High-precision absolute (true) density measurements on hygroscopic powders by gas pycnometry: application to determining effects of formulation and process on free volume of lyophilized products. J Pharm Sci. 2011 Jul; 100(7):2945-51.