What is the difference between hygroscopic and deliquescent?
A hygroscopic substance takes up water from the air; a deliquescent one takes up so much that it dissolves in it, above its critical relative humidity. Lyophilised peptides are hygroscopic: an opened cold vial can gain water within minutes, changing weighed mass and speeding degradation. Warm vials before opening and reseal promptly.
How are the terms defined?
| Term | Meaning |
|---|---|
| Hygroscopic | Absorbs or adsorbs water vapour from air |
| Deliquescent | Absorbs enough water to dissolve, above a critical humidity |
| Critical relative humidity (CRH) | Humidity above which a solid deliquesces |
| Efflorescent | Loses water of crystallisation to air |
| Water activity (aw) | Relative vapour pressure of water in a sample |
Why are lyophilised peptides hygroscopic?
Freeze-dried solids are amorphous with large surface area, and peptide counter-ions such as acetate and trifluoroacetate add polarity. Moisture lowers the glass transition temperature and increases mobility, which accelerates degradation in the solid state.
Source: Efficient throughput method for hygroscopicity classification of pharmaceutical ingredients, Pharm Dev Technol 2013 (PubMed 21981708); Stability of protein pharmaceuticals: an update, Pharm Res 2010 (PubMed 20143256)
How does moisture affect weighing?
- Mass drifts upwards on the balance as water is absorbed.
- Water content (Karl Fischer) on a CoA explains part of the gap between gross weight and net peptide.
- Weigh quickly, in low humidity, after the vial reaches room temperature.
How does Sable document lots?
There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.
Frequently asked questions
What does hygroscopic mean?
That a substance takes up water vapour from the air.
What does deliquescent mean?
That a solid absorbs so much water it dissolves, above its critical relative humidity.
Are lyophilised peptides hygroscopic?
Yes; warm vials before opening to avoid condensation.
Related
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- Hygroscopic: takes up water
- Deliquescent: dissolves in absorbed water above CRH
- References: PubMed 21981708, 20143256
- Updated 2026-10-16