- Document
- ST-05
- Section
- Storage fundamentals
- Revised
- Sources checked
- Bands
- −20 °C2–8 °C15–25 °C
Moisture and Humidity: Keeping Dry Material Dry
Water undoes the benefit of lyophilization. Where moisture gets in, why opening a cold vial is the biggest risk, and how to use desiccants properly.
Bench card
- The most common moisture event is condensation on a cold vial opened too soon.
- Always equilibrate vials to room temperature in a desiccator before opening.
- Store lyophilized vials in a sealed secondary container with active desiccant.
- Humidity also affects weighing: hygroscopic powder gains mass while it sits on the balance.
- Replace or regenerate desiccant when its indicator changes colour.
Lyophilized peptides last because they are dry. Anything that lets water back in, even a little, speeds up degradation and makes weighing unreliable. Most moisture problems are easy to prevent once you know where water comes from.
Where moisture comes from
- Condensation: a vial straight from −20 °C is far below the dew point of room air. Open it and water condenses on the cold powder immediately.
- Room air: every opening exchanges headspace with humid lab air.
- Imperfect seals: stoppers and screw caps let small amounts of vapour through over long periods, more so after repeated punctures or openings.
- Freezer frost: boxes stored in a frosty freezer pick up ice that melts when the box is opened.
Why a little water matters
Water acts as a plasticizer in amorphous solids: it increases molecular mobility and lowers the glass transition temperature, letting reactions proceed that are almost frozen in a dry cake. Studies on lyophilized proteins have found that degradation rates increase with residual moisture. The exact relationship varies by molecule and formulation, so the safest rule is to keep exposure to a minimum.
The equilibration rule
Using desiccants
| Desiccant | Strengths | Watch for |
|---|---|---|
| Indicating silica gel | Cheap, shows saturation by colour change | Capacity falls at low temperature; replace or regenerate when the colour changes |
| Molecular sieve | Holds water strongly at low humidity | No visual indicator unless one is added |
| Calcium sulfate | Fast and inert | Lower capacity |
Put vials and desiccant together in a sealed secondary container such as a screw-top jar or a heat-sealable foil pouch, rather than loose in a freezer box. Add a humidity indicator card if you want a visible check.
Weighing hygroscopic powder
- Equilibrate the vial as above.
- Weigh by difference: weigh the closed vial, remove material, and weigh again. This limits how long powder is exposed.
- Work in low humidity if possible, or under a dry nitrogen stream for very sensitive material.
- Remember that the weighed mass includes water and counterions. Use the COA’s net peptide content where an exact amount of peptide matters. See Purity Terminology.
References
- Wang W. Lyophilization and development of solid protein pharmaceuticals. Int J Pharm. 2000;203(1–2):1–60. DOI
- Breen ED, Curley JG, Overcashier DE, Hsu CC, Shire SJ. Effect of moisture on the stability of a lyophilized humanized monoclonal antibody formulation. Pharm Res. 2001;18(9):1345–1353. PubMed
- Carpenter JF, Pikal MJ, Chang BS, Randolph TW. Rational design of stable lyophilized protein formulations: some practical advice. Pharm Res. 1997;14(8):969–975. DOI
- USP General Chapter <921> Water Determination. United States Pharmacopeia.