A lyophilized peptide arrives as a small disc or film of white powder at the bottom of a sealed vial. Bringing it into solution is straightforward, but a few details separate a clean reconstitution from a partially degraded one.
Start by letting the vial reach room temperature before opening it. Condensation forming on cold powder introduces water in an uncontrolled way, and moisture is what shortens the shelf life of a lyophilized product. Wipe the stopper of both the peptide vial and the bacteriostatic water with an alcohol swab and let them dry.
Draw the volume of bacteriostatic water your protocol calls for, then direct the stream against the inside wall of the vial rather than straight down onto the powder. The peptide should dissolve on its own within a minute or two; swirl gently if it needs help. Do not shake. Agitation shears peptide bonds and produces the faint cloudiness that indicates a partially denatured solution.
Label the vial with the date of reconstitution and return it to the refrigerator. The certificate of analysis for that lot states how long the solution remains within specification — that figure, not a general rule of thumb, is the one to work to.