Model development for O(2) and N(2) permeation rates through CZ-resin vials

The headspace of vials containing oxygen-sensitive formulations is filled with a nitrogen blanket. This paper presents the development of a mathematical model to predict the oxygen and nitrogen permeation rates through the walls of plastic CZ-resin vials. The model estimates the time required for a nitrogen-filled vial to reach ambient nitrogen and oxygen levels. The permeation of oxygen and nitrogen through the vial is governed by Fick's law and may be described by an exponential equation. Using the values for oxygen and nitrogen permeation through CZ-resin vial, the half-lives for the decrease in nitrogen level and increase in oxygen level was found to be 150 days and 15 days, respectively. This result can be attributed to the greater permeability of CZ-resin vial to oxygen (79.06 cm(3)-mm/m(2)-24 h-atm) when compared with nitrogen (12 cm(3)-mm/m(2)-24 h-atm). The ingress of oxygen into CZ-resin vials was determined experimentally and it was found to verify the model. These results indicate that CZ-resin vials may be inappropriate for packaging oxygen-sensitive formulations even in the presence of a nitrogen-filled headspace.