Powder vs mixed vial: keeping peptides cold, dry and happy

Why dry beats wet

Water is what most degradation reactions need. Freeze-drying pulls nearly all of it out, which is why powder ships well and keeps far longer than the same peptide in solution. It is also the reason to mix only what the work in front of you needs.

Looking after powder

• Leave the seal intact until mixing day.
• Keep it in the fridge, or at about -20°C or colder for longer stretches^[1].
• Let a cold vial warm to room temperature before opening it, so moisture doesn't condense on the powder^[1].
• Keep vials boxed or otherwise in the dark.

Looking after a mixed vial

• Keep it refrigerated rather than on the bench.
• Avoid repeated freezing and thawing^[1].
• If the vial will be entered more than once, mix with bacteriostatic water; we recommend the Hospira 30 mL. The 3 mL vs 30 mL guide explains why.
• Label it with the mixing date and concentration (our Lab Calculator does the math).
• Discard it if it turns cloudy, changes color or shows particles.

So how long does it last?

There is no single answer: it depends on the sequence, and peptides containing residues such as Cys, Met, Trp, Asn or Gln are less stable in solution^[1]. Check the paperwork for the specific compound. As a rule of thumb, cold, dry powder outlasts the same peptide once mixed by a wide margin. And remember the 28-day window often quoted for bac water applies to the water vial after first puncture, not to the mixed peptide.