The vial: glass, stopper and seal
A lyophilized peptide is typically supplied in a small crimp-top vial of three parts that each do one job: a Type I borosilicate glass body, an elastomer stopper designed for freeze-drying, and an aluminium crimp seal with a flip-off cap.
The glass holds the dried cake and releases very little of itself into it. The stopper closes the vial and, earlier, lets water vapour leave during drying. The crimp keeps the stopper under compression and shows whether the cap has been disturbed.
The glass body
Type I borosilicate is the glass class with the highest hydrolytic resistance, a measure of how much alkali a glass releases into water in a standardised extraction test. The classes are defined in USP <660> and Ph. Eur. 3.2.1. Two properties explain the choice: low alkali leaching, and low thermal expansion. The second lowers the risk of cracking under the temperature changes of freezing and drying.
Glass is supplied clear or amber; clear allows the cake to be seen. Amber glass is specified by a maximum light transmission between 290 and 450 nm, so it is chosen where a compound is light-sensitive. The companion article, Light and peptides, covers that case.
The stopper
Vial stoppers are typically bromobutyl or chlorobutyl rubber, halogenated butyl elastomers chosen for low permeability to gas and water vapour. The freeze-drying design adds slots or legs. During drying the stopper sits partly inserted in the neck, and the gaps let water vapour escape from the vial. When drying ends, the shelves of the freeze-dryer press each stopper fully home while the vials are still inside the chamber.
Some stoppers also carry a film coating that reduces sticking and the amount of material that can be extracted from the rubber. A stopper can itself hold water and release it into the cake during storage.
The crimp seal
An aluminium crimp is folded over the stopper and the rim of the neck, holding the stopper under compression against the glass. A plastic flip-off cap sits on top of the aluminium. A missing or loose cap shows that tamper evidence has been lost. The headspace is often backfilled with nitrogen to below atmospheric pressure or left under partial vacuum, which is why a stopper can look pulled inward.
What visual inspection can show
Solara labels each vial with the compound name, the quantity in milligrams, the form, an expiry date and "for research use only". Visual inspection can detect some closure and cake defects:
- A stopper fully seated under the crimp, not sitting proud.
- An intact crimp with no gaps, dents or loose edge, and the flip-off cap present.
- A cake that looks like a dried plug rather than a collapsed or wet-looking mass.
- No foreign matter visible in the vial.
- A legible label with the expiry date readable.
Solara has not published container closure integrity test data or the glass and stopper specification for its vials.
What this does not establish
- A sound container does not establish the purity or identity of the contents; those need analytical methods such as HPLC and mass spectrometry.
- An intact seal does not demonstrate sterility, and Solara does not claim sterility for its vials.
- Glass type is a specification of the container, not of the peptide, and says nothing about the stability of any compound.
Questions
What is Type I glass?
Why does the stopper on a lyophilized vial look different from a liquid vial's stopper?
Why does a vial sometimes seem to be under vacuum?
References
- Sacha GA et al. Practical fundamentals of glass, rubber, and plastic sterile packaging systems. Pharmaceutical Development and Technology, 2010.
- Pikal MJ et al. Moisture transfer from stopper to product and resulting stability implications. Developments in Biological Standardization, 1992.
- Container Closure Systems for Packaging Human Drugs and Biologics (guidance). US Food and Drug Administration, 1999.
Every compound on this site is supplied as a lyophilized powder for laboratory research use only. Nothing in this article describes an effect on a person or is a claim about any product.