Most of the variance people attribute to a batch is not the batch. It is what happened in the ninety seconds after the vial was opened.
Bacteriostatic, not sterile
Use bacteriostatic water — sterile water with a preservative, usually 0.9% benzyl alcohol. Plain sterile water has nothing in it to stop growth once the seal is broken, which is fine for a single dose and wrong for a vial you will return to for three weeks.
Down the side, then swirl
Add the water down the inside wall of the vial rather than directly onto the powder, and let it dissolve. Then swirl. Never shake.
Agitation shears the peptide, and this is the part that catches people out: you cannot see it happen. The solution looks identical either way. A vial that was shaken and a vial that was swirled are indistinguishable in the hand and not indistinguishable in effect.
Concentration is arithmetic, not judgement
Work out the concentration before you draw anything. Total milligrams divided by millilitres of water gives you mg/ml; from there the volume for a given dose is one division. Do it on paper once and write the result on the box — not in your head at the moment you need it.
How long it actually keeps
Reconstituted, stability is measured in weeks under refrigeration at 2-8°C, not months. Sealed and frozen, most lyophilised peptides hold for far longer. Do not refreeze a solution that has already been made up.
Label the vial with the date you opened it. Memory is not a storage protocol, and a vial with no date on it is a vial you will eventually have to throw away on principle.
