A lyophilized peptide is a fragile powder. How you dissolve it determines whether your material stays intact, and whether your concentration matches what you think you have.
Method
First let the vial come to room temperature; cold glass causes condensation, and condensation brings moisture into the powder. Then add the solvent slowly along the wall of the vial, so the stream doesn’t hit the powder directly and it doesn’t foam. Next, swirl the vial gently until everything has dissolved. Do not shake.
A clear, colorless solution without floating particles is what you want to see. If material remains or the solution looks cloudy, let the vial stand a little longer before you continue.
Calculating the concentration
Divide the amount of peptide by the volume added. Ten milligrams in two milliliters gives five milligrams per milliliter.
How much solvent
More solvent gives a lower concentration and so larger volumes per draw, which allows more accurate measuring. Less solvent gives smaller volumes, where a small reading difference weighs relatively heavier. So choose the volume based on the amount you work with, not on what happens to fit in the vial.
Common mistakes
- Shaking instead of swirling. That causes foam, and foam means peptide stays behind at the interface.
- Aiming the stream straight at the powder. This makes the material clump and dissolving takes needlessly long.
- Calculating with the vial weight instead of the peptide weight. Salts and residual moisture count toward the weight, but not toward your concentration.