Buyers ask how long a lyophilized peptide lasts, and the honest answer has three parts: what is actually happening in a dry vial, where a printed expiry date comes from when there is one, and why the certificates on this site carry an issue date instead. The storage guide covers the practical rules and the reconstituted shelf-life post covers the solution; this post is about the sealed, dry vial before anyone opens it.
What is actually degrading in a dry vial?
The same reactions as in solution, running far slower. Lai and Topp's 1999 review of solid-state peptide and protein stability lists them: deamidation of asparagine and glutamine, isomerisation and cleavage at aspartate, oxidation of methionine, cysteine, tryptophan and tyrosine, disulfide scrambling, and non-enzymatic reactions with any reducing sugar present. In a lyophilized cake the molecules are immobilised in a glassy solid, reactants cannot diffuse to one another, and rates fall by orders of magnitude. They do not fall to zero.
Which reactions matter depends on the sequence, which is why the handling section of every compound post on this site names the reactive residues. MOTS-c, with two methionines, and humanin, with a cysteine, have a route a tripeptide like pinealon does not. The oxidation post is the full list.
Why residual water is the controlling variable
Freeze-drying does not remove all the water. Tang and Pikal's practical guide puts typical residual moisture after secondary drying at around one percent or less, and a cake that has been opened in humid air or stored with a poor seal can climb to several percent. That difference is the whole story of solid-state stability. Water plasticises the glass: above a threshold the cake's glass transition falls toward room temperature, the solid becomes mobile on a molecular scale, and the reactions above resume at a meaningful rate. Water is also a reactant in hydrolysis and deamidation.
Three consequences follow for a sealed vial.
- Temperature matters mostly through the glass transition. A cake at minus 20 °C is far below its transition whatever its moisture; at room temperature a moist cake may be near it.
- The seal matters as much as the freezer. A crimped stopper that holds is what keeps moisture out. The vial appearance post covers what a compromised seal looks like.
- Opening the vial resets the clock. Each entry admits humid air. A vial opened once and resealed is no longer the vial the laboratory tested, which is why the storage post recommends aliquoting on first use.
What accelerated studies predict, and what they cannot
A pharmaceutical expiry date comes from a stability programme designed to the ICH Q1A(R2) guideline: the material is stored at its labelled condition and measured at intervals for the whole proposed shelf life, and in parallel stored at a higher temperature and humidity, typically 40 °C and 75% relative humidity, to force degradation faster. The accelerated data are extrapolated to the labelled condition using the Arrhenius relationship between rate and temperature, and the real-time data confirm or correct the prediction as they arrive. The stability study post describes how to run the same design in a research setting.
The method is good at one thing and poor at another. It predicts well when the degradation route is the same at both temperatures and follows simple kinetics, which is often true of deamidation and oxidation in a stable glass. It predicts badly when the accelerated condition crosses the glass transition, which changes the mechanism, or when a route that is negligible at 40 °C dominates at 5 °C, or when the vial's seal rather than its chemistry is what fails. A printed "24 months at 2 to 8 °C" is therefore a claim about a specific formulation, container and closure, tested by a specific programme. It does not transfer to a different fill in a different vial.
What a retest date means, versus an expiry
Two different claims that are often confused.
| Date type | What it says | Who uses it |
|---|---|---|
| Expiry | Do not use after this date | Finished pharmaceutical products |
| Retest | After this date, re-measure the material before use; it may still meet specification | Drug substances and reference materials |
A research reagent, when it carries any date, usually carries a retest date, and the right response to passing it is a measurement, not disposal. For a peptide that means re-checking identity by mass and purity by HPLC, which is what the independent testing post describes, or at minimum the bench checks in the purity test kit post.
Why these certificates carry an issue date and no expiry
Every certificate in the COA library reports identity, purity, content and endotoxin for a lot, and the date the laboratory issued the report. None reports an expiry or a retest date, because the laboratory measured the lot once and did not run a stability programme on it. A shelf-life figure on such a certificate would be a prediction dressed as a measurement. The issued-date post is the longer treatment of why the date is the honest field and how to read it.
The practical reading is this. The certificate tells you what the lot was on its issue date. The sequence tells you which routes it is exposed to. Storage, which the buyer controls, decides how far it has moved since. A sealed vial held at minus 20 °C in the dark with its crimp intact moves very little over a year for most sequences, and the cold-shipping post explains why a few days at ambient temperature in transit does not change that. A vial opened, warmed and resealed is a different object, and the certificate never claimed to describe it.
Frequently asked questions
Does a lyophilized peptide expire?
It degrades, slowly, by routes set by its sequence and at a rate set by moisture and temperature. Whether it has "expired" is a question about a specification and a measurement, not a date on its own.
Why is there no expiry date on the certificate?
Because the laboratory measured the lot once, on the issue date, and did not run the stability programme an expiry claim requires. The certificate reports what was measured.
What is the single most important storage variable for a sealed vial?
Moisture, through the seal. Temperature matters mostly by keeping the dry cake well below its glass transition.
Can I use a peptide after a supplier's printed date?
If the date is a retest date, re-measure identity and purity and decide on the result. If it is an expiry on a pharmaceutical product, the manufacturer's instruction is not to.
What happens when the vial is opened?
Humid air enters and the moisture clock restarts. Aliquot on first use so that the bulk of the lot is never opened twice.
References
- International Council for Harmonisation. ICH Q1A(R2): Stability Testing of New Drug Substances and Products. 2003. www.ich.org/page/quality-guidelines
- Lai MC, Topp EM. Solid-state chemical stability of proteins and peptides. Journal of Pharmaceutical Sciences 1999;88(5):489-500. doi.org/10.1021/js980374e
- Tang X, Pikal MJ. Design of freeze-drying processes for pharmaceuticals: practical advice. Pharmaceutical Research 2004;21(2):191-200. doi.org/10.1023/b:pham.0000016234.73023.75
Every product mentioned is sold for laboratory research use only and is not for human or animal use. Nothing on this page describes or recommends use of the material sold here in humans or animals.
