Dry pharmaceutical product needs to be protected from moisture to achieve an optimal shelf life. Sterile injectable products such as freeze dried formulations or dry powders are often sealed in stoppered vials under dry nitrogen. Over the shelf life of the product it is possible for moisture to permeate into the vial. The LIGHTHOUSE method for non-destructive headspace analysis enables headspace monitoring over the full shelf life in a single vial. This in turn enables very accurate determination of permeation rates of potentially reactive gases such as water vapor and oxygen during the product shelf life. Such information can be critical for QC groups performing stability studies, or for packaging development groups responsible for choosing the optimal primary packaging configuration.