The peptide vial: septum, crimp and vacuum seal explained

The small glass vial a research peptide arrives in is doing more than holding powder. Its stopper, crimp and internal vacuum are what keep the lyophilised cake dry and sterile from the filling line to your bench, and understanding them tells you how to open a vial correctly and how to spot one that has been compromised. This note explains the components, what the vacuum is for, and how to handle the vial from arrival to first puncture. All Alphex products are for laboratory and in-vitro research only.

The parts

• The vial. Borosilicate glass, typically 2 mL or 3 mL for peptide fills, chosen because it is inert, transparent for inspection, and does not release extractables into the contents.
• The stopper. A bromobutyl or chlorobutyl rubber plug with a thin central diaphragm designed to be pierced by a needle and to reseal around it. Butyl rubber is used because it is a poor gas and moisture barrier only in the sense of being very good: little water vapour or oxygen crosses it.
• The crimp cap. An aluminium ring, usually with a plastic flip-off disc, crimped over the stopper to hold it under compression against the vial lip. The disc protects the septum from contamination; it is not the seal.
• The vacuum. Peptide vials are stoppered inside the freeze-dryer at the end of the lyophilisation cycle, while the chamber is still under partial vacuum. The vial is therefore sealed with less than atmospheric pressure inside, and often with a nitrogen backfill.

What the vacuum does

Sealing under vacuum or nitrogen removes most of the oxygen and water vapour from the headspace, which is why lyophilised peptides are so stable in the closed vial: the two ingredients most degradation needs are simply not present. It also gives you a built-in integrity check. A vial that is still under vacuum has a stopper that sits slightly concave, and when you first puncture it you feel or hear air rush in. If you insert a syringe already filled with diluent, the vacuum will pull the liquid in faster than you push, which is one reason to add diluent slowly and against the vial wall.

Handling from arrival

1. Inspect. Label present and legible with batch number; crimp intact; flip-off disc in place; stopper slightly domed inward; cake, film or flakes visible (a shifted or broken cake is normal). See what lyophilised means.
2. Store sealed. -20 C in the dark until needed. Do not remove the flip-off disc until reconstitution.
3. Warm before opening. 15-20 minutes at room temperature so condensation does not form on the cold cake when air enters.
4. Flip off the disc, swab the septum with 70% alcohol, let it dry.
5. Puncture once, centrally, at a slight angle so the needle tip rests against the inside wall, and add diluent slowly. Repeated punctures in the same spot core the rubber and can drop fragments into the vial; use a fresh entry point for subsequent withdrawals and prefer fine-gauge needles.
6. After reconstitution the septum still reseals, so a stock can be sampled repeatedly through it. Swab before each entry.

Signs of a compromised vial

• Stopper flat or domed outward, or no air rush on first puncture: vacuum lost. The cake may have taken up moisture. Contact us with the batch number before using.
• Loose or rotating crimp, or a stopper that can be lifted: seal failed.
• Cracked glass, or powder outside the vial in the packaging.
• Discoloured cake, or a cake that has visibly collapsed into a glassy droplet: moisture ingress.

Alphex ships vials in a rigid inner box inside a padded outer, and replaces any vial that arrives compromised.

Frequently asked questions

Can I remove the stopper entirely?

You can, but you lose the seal and the ability to sample aseptically. Reconstitute through the septum instead.

Why is there so little in the vial?

Because 5-10 mg of freeze-dried peptide is a tiny, low-density solid, often a film. It is normal.

Does the septum leach anything?

Butyl rubber is chosen for very low extractables. For ultra-sensitive analytical work, prepare samples in the assay tube rather than storing dilute solutions in the vial long term.

Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They are not authorised for human or veterinary use.

Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.

Published 13 July 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.

Alphex Research Team

Alphex Limited, UK research peptide supplier

The Alphex research team writes and maintains these notes for UK laboratories buying research peptides. Every batch Alphex lists is verified by reverse-phase HPLC with a batch-matched Certificate of Analysis. Content covers laboratory and in-vitro research only.