Vial filling and stoppering (revision 6)

Vial filling and stoppering is the operation that transfers material into its final container and closes it. For a lyophilised product the sequence is distinctive: solution is filled, stoppers are seated only partially so that vapour can escape, the vials are dried in the chamber, and the stoppers are then pressed home before the vials leave it.^[1]

Two attributes are set here and nowhere else. Fill mass determines how much material a purchaser receives — see Underfilling — and container closure integrity determines whether the contents stay dry and uncontaminated for the shelf life.^[2]

Neither is visible in a chromatographic determination. A certificate reporting purity describes the material; it says nothing about how much of it is in the vial or whether the vial is sealed.^[3]

Filling is volumetric or gravimetric. Volumetric filling meters a volume and relies on solution density; gravimetric filling weighs, in-process or in a sampling plan, and is more directly connected to the quantity of interest.^[1]

Fill accuracy is specified as a tolerance and monitored during the run, since pump and valve behaviour drifts, and the in-process records are part of the batch documentation.^[4] A deliberate overage above the label claim is ordinary and compensates for losses in reconstitution and withdrawal; it is not a defect. See Underfilling.

For a peptide the mass of interest is peptide mass, which is fill mass multiplied by content. A fill process controlled to a tight tolerance on solid mass still delivers a variable peptide mass if content varies between lots, which is why content belongs on the certificate alongside purity.^[3]