Knowledge Center

Lyophilization: why peptides ship as powder

Lyophilization is freeze-drying. A solution of purified peptide is frozen, a deep vacuum is pulled, and the ice sublimes — passes straight from solid to vapor — leaving the peptide behind as a dry, porous cake at the bottom of the vial.

The point is stability. In water, peptides slowly hydrolyze, oxidize, and clump into aggregates. Remove the water and those processes slow to a crawl, which is what lets a peptide be made in one place, tested by an independent laboratory in another, and arrive at yours unchanged.

One fact to carry out of this section: the cake is not pure peptide by weight. It also holds the counterion from synthesis and a little residual water, which is why the mass on the label and the net peptide content on the certificate are different numbers.

Net peptide content, explained

Reconstitution is a laboratory operation

Reconstitution is the reverse operation: a measured volume of diluent goes in through the septum and the cake returns to solution. Two diluents dominate bench practice. Sterile water is exactly that — water, sterilized, nothing added. It carries no preservative, so it suits work that opens a vial once and uses the solution promptly. Bacteriostatic water is sterile water plus 0.9% benzyl alcohol, a preservative that suppresses microbial growth so a sealed vial can be sampled more than once over a working period. Benzyl alcohol also interferes with some assay systems, and that fact alone settles the choice for many researchers.

Which diluent, and how much of it, are decisions this site never answers. The volume added is simply another way of stating the concentration your own work requires, and only that knows the figure. What we can state are the facts that protect the material: run the diluent down the inside wall of the vial rather than onto the cake, then swirl gently until the solution is clear. Shaking whips air into the liquid, and peptides denature at the air–liquid interface of a foam.

Storage and stability

The dry state and the dissolved state have different stability stories. Keep them separate.

Lyophilized is the long-term state. Standard practice for the sealed cake is a freezer at −20 °C, dark and dry. Light drives oxidation of sensitive side chains — the reason amber glass and foil wraps exist — and moisture is the enemy the whole lyophilization effort was aimed at, so the intact seal matters as much as the temperature. Avoid cycling a vial between freezer and bench: condensation forms on cold glass, and repeated warm-ups age material faster than steady cold does.

In solution the clock runs faster: refrigeration at 2–8 °C, protection from light, and as few freeze–thaw cycles as possible — ideally none, which is what single-use aliquots frozen once are for. And there is no universal shelf life. Stability belongs to a specific molecule in a specific state under specific conditions; a figure that claims to cover “peptides” in general deserves your suspicion, from any supplier.

Cold chain, and what arrives in the box

Lyophilization is also what makes transit survivable. The dry cake tolerates the temperature swings of shipping far better than any solution could, so cold packaging in the box is margin on top of that stability, not a rescue of it.

What arrives is the sealed system itself: crimped vials, each labeled with the article name, its mass and net peptide content, the caution statement, and a code that resolves to the record for that exact lot.

Two arrival habits serve you well. Look at the cake first: it should sit as an intact, dry plug. A collapsed, gummy, or partly dissolved cake suggests a serious temperature excursion and is worth reporting before the vial is used. Then move the vial to its long-term storage rather than leaving it on the bench.

CAUTION: Contains a new drug for investigational use only in laboratory research animals or for tests in vitro. Not for use in humans.

Shipping and cold chain

Vial, stopper, septum

The container is a three-part system: a glass vial, an elastomer stopper, and an aluminum crimp that holds the stopper in compression. The stopper’s center is the septum — a region made to be pierced and to reseal, so the vial can be entered without ever being opened. The flip-off cap on top is a dust cover, nothing more; once it is gone, the cleanliness of the septum surface is your bench practice’s job, not the cap’s.

Every entry through the septum is an event in the vial’s history — elastomers reseal well, but not infinitely, which is one reason single-entry practice and aliquots exist. The seal itself is a tested attribute: container closure integrity, whether the sealed vial stays sealed against moisture, is one of the fourteen tests in the quality framework.

Container closure integrity, and the other thirteen

The lot ties the vial to its certificate

A lot is one production run of one article, made together and tested together. Every vial filled from that run carries the same lot number, and the independent laboratory issues one certificate of analysis for the whole lot, hosted on the laboratory’s own systems — the numbers you read are the numbers it measured.

So the code on your vial is not an inventory sticker. It is the key that retrieves the test record for exactly the material in your hand. The record runs in both directions — lots that failed never shipped, and their records are published too.

Verify a certificate · Failed lots

Where the calculator fits

Concentration arithmetic has three quantities — a mass of peptide, a volume of diluent, and the concentration that results — and fixing any two determines the third. The calculator computes that third number and does nothing else. It has no defaults and makes no recommendations; every value in it is one you typed. Its one piece of guidance concerns which mass to use: if your work depends on the peptide actually present rather than the label figure, carry the certificate’s net peptide content into the arithmetic.

Open the calculator