Peptides are stored in a lyophilized (a freeze dried fine powder) state and so need reconstitution before they can be used. Sterile water with a bacteriostatic agent (0.9% Benzyl Alcohol) added is generally (except for IGF1 type peptides, see below) the best choice, as it both extends the storage life of the reconstituted product and also allows multiple doses to be drawn up out of the vial, which is more convenient and cost-effective in a research context. However, for IGF1 DES and IGF1 Long R3, Acetic Acid 0.9% should be used for reconstitution due due to buffering issues and poor solubility when using bacteriostatic water.
Looking at the various diluting agents in more detail:
This is a sterile, nonpyrogenic preparation of water for
injection containing 0.9% (9 mg/mL) of benzyl alcohol added as a bacteriostatic
preservative. It is supplied in a multiple-dose container from which repeated withdrawals
may be made to dilute or dissolve drugs for injection. The pH is 5.7 (4.5 to
Bacteriostatic water is used to reconstitute all peptides, although
for IGF1 derivatives Acetic Acid is recommended.
Acetic acid is the second simplest carboxylic acid (after
formic acid). It consists of a methyl group attached to a carboxyl group.
Acetic acid should be used to reconstitute IGF1 derivative
peptides, as they dissolve more readily and remain stable for longer in storage.