Cold Chain and Temperature Excursions in Transit
Research peptides are frequently shipped without refrigeration, which looks careless next to the storage advice on the vial. The reconciliation is that the dry state and the dissolved state have very different tolerances, and transit is short.
Why the dry state travels well
Most degradation routes in peptides need water. Hydrolysis needs it directly; deamidation proceeds through a hydrated intermediate; disulfide exchange requires mobility that a dry solid does not provide. Remove water and the reaction rates fall by orders of magnitude.
A properly lyophilised cake with low residual moisture is therefore far more tolerant of warmth than the same material in solution. Days at ambient temperature produce changes that would take a solution hours. Lyophilisation and the cake in the vial covers the dry state, and water content covers the measurement that establishes how dry it actually is.
The caveat is that “low residual moisture” is a property of the specific lot rather than of lyophilised material in general. A collapsed or under-dried cake carries more water and travels less well.
Mean kinetic temperature
Storage conditions are not well described by an average. Degradation accelerates exponentially with temperature, so an hour at 40 degrees contributes far more than an hour at 20 saves.
Mean kinetic temperature is the single temperature that would produce the same cumulative degradation as the varying profile actually experienced. It is always higher than the arithmetic mean, and the gap widens with the size of the excursions. A shipment averaging 22 degrees with brief peaks at 45 has a mean kinetic temperature well above 22.
It is the correct way to think about a transit record, and it explains why a short severe excursion matters more than a long mild one.
What an excursion actually threatens
For a dry, well-sealed vial, brief warmth is usually inconsequential. The conditions worth attention are different:
- Warmth with moisture. A compromised seal admits humidity, and warmth then acts on a hydrated solid. The combination is what does damage, not heat alone. Vial closures and headspace covers seal integrity.
- Freezing in transit with condensation on arrival. A vial arriving frozen and opened immediately collects water on cold solid. Weighing lyophilised peptides covers what that does to a mass measurement.
- Prolonged exposure. A package delayed for weeks in a warm environment is a different proposition from two days in transit.
On arrival
Allow the vial to equilibrate to room temperature before opening it, inspect the cake and the seal, and record the condition before storage. Checks to run when a shipment arrives covers the sequence, and storage stability covers conditions once it is put away.
All material is supplied for laboratory research use only. It is not a drug, not a supplement, and not for use in humans or animals.
