Reconstituting Lyophilized Peptides: The Math and the Method

Reconstitution has a reputation for being fiddly, but there are only two parts to it: a bit of arithmetic, and adding liquid without beating up the powder. Do both well and the job takes a couple of minutes. Get either one wrong and you end up with a concentration you can't vouch for, or material that has started to break down. Neither gives you clean data.

Below is the full process for an ordinary lyophilized research vial. The math comes first, because it's the step people rush and then wish they hadn't.

What to have on the bench

• The lyophilized vial, kept cold up to this point
• Bacteriostatic water, or sterile water if the solution won't be kept long
• A sterile pipette or sterile transfer device for measuring the diluent
• Alcohol swabs and a clean surface out of any draft

Work out the concentration before anything else

Concentration is mass over volume, nothing more. The mass is already set: it's the amount printed on the vial. The only variable you control is the volume of diluent. Less liquid gives a stronger solution, more liquid gives a weaker one.

Pick the concentration you want first, then add whatever volume gets you there. For a 10 mg vial:

• 1 mL — 10 mg/mL, a concentrated stock for small working volumes
• 2 mL — 5 mg/mL, a middle-of-the-road stock that's easy to measure from
• 5 mL — 2 mg/mL, a dilute stock for finer measurement and larger volumes

Note: choose a volume that makes the amounts you'll pipette for your assays easy to measure accurately. Clumsy numbers at the bench are where errors creep in.

Step by step

1. Let things warm up. Leave the cold vial out for a few minutes first. Liquid added to very cold glass encourages condensation and the powder dissolves more slowly.
2. Wipe the stoppers. Swab the top of the peptide vial and the diluent vial with alcohol and let them air-dry.
3. Measure the diluent. Take up exactly the volume your concentration math called for.
4. Add it slowly down the side of the vial. Tilt the vial and let the liquid run down the glass rather than landing straight on the powder cake. A forceful stream can foam the solution or disturb the cake, so go gently.
5. Give it time to dissolve. Wait a minute, and swirl softly if it needs help. Don't shake it; shaking causes foaming and stresses the peptide. The finished solution should be completely clear.
6. Label it and get it cold. Write the concentration and the date on the vial and put it in the fridge. You won't remember either detail next week.

Mistakes that cost you a vial

• Shaking rather than swirling. Foam forms, some peptide denatures, and material is lost at the meniscus.
• Squirting the diluent straight onto the powder instead of down the glass.
• Guessing the volume, which leaves you with no real idea of the concentration.
• Not labelling. A week on, an unmarked clear vial in the fridge tells you nothing at all.

Note: for research use only. This is general lab-handling information and is not guidance for human or veterinary use.

FAQ

Which water is used to reconstitute a peptide?

In research settings the usual pick is bacteriostatic water. Its benzyl alcohol slows microbial growth, which matters for a solution kept in the fridge over a period of time. For short-term work, sterile water is fine.

How is the concentration calculated?

Take the peptide mass on the vial and divide it by the volume of water you add. A 10 mg vial with 2 mL added comes out at 5 mg/mL. Work backwards from the concentration you want to get the volume.

Is it OK to shake the vial so it dissolves faster?

No. Shaking makes the solution foam and can denature the peptide. Swirl it gently and be patient; most peptides dissolve within a minute or two.

Related guides

• Storage and stability after reconstitution