Abstract
Lyophilisation removes water by sublimation under vacuum, producing a dry solid with improved storage stability. This article explains the process, the appearance of the resulting cake, and the handling considerations it implies.
Most research peptides are supplied as a lyophilised solid rather than a solution. The reason is stability: removing water suppresses hydrolysis and other water-mediated degradation routes, and a dry solid tolerates transport far better than a cold liquid.
How lyophilisation works
The solution is frozen, then placed under reduced pressure so that ice sublimes directly to vapour without passing through a liquid phase. A secondary drying stage removes residual bound water. Because the material never returns to a concentrated liquid state, thermal and chemical stress are lower than in evaporative drying.
- Freezing stage: the solution is cooled below its eutectic point
- Primary drying: ice sublimes under vacuum at controlled temperature
- Secondary drying: residual bound water is removed
- Stoppering and sealing under controlled atmosphere
Reading the cake
The dried product forms a porous cake whose appearance carries information. A uniform, intact cake indicates a well-controlled cycle. Collapse, shrinkage, or a glassy layer suggests the product temperature exceeded its critical value during drying. Very small quantities may appear as a thin film or as barely visible residue, which is normal and not an indication of a missing fill.
For low-milligram fills, an apparently empty vial is usually a correctly filled one; the cake is simply thin.
What remains after drying
Lyophilisation does not produce an anhydrous solid. Residual water, residual solvents from purification, and counter-ions such as acetate or trifluoroacetate remain part of the total mass. This is why the mass in a vial and the net peptide mass are distinct quantities, and why documentation reporting both is more informative than a single figure.
Handling on arrival
Because the cake is hygroscopic, it should be equilibrated to ambient temperature before the closure is broken, then reconstituted promptly with the solvent appropriate to the intended method. Recording the appearance of the cake on receipt takes seconds and provides a useful reference if the material later behaves unexpectedly.
