Reconstitution is just dilution math

Lyophilized peptides are freeze-dried so they ship as a cake instead of a fragile solution. Reconstitution means adding a known volume of solvent, dissolving the cake, and calculating how many micrograms sit in a known number of insulin-syringe units. That is dimensional analysis — the same family of math you use to prepare any known concentration for an assay.

The numbers that matter

Mass on the vial (mg). Volume of diluent (mL). Desired mass in the aliquot (mcg). A U-100 syringe is 100 units per milliliter. So: mcg per mL = (mg × 1000) / mL. Units = desired mcg / (mcg per mL) × 100. Read that as a dilution formula. The “desired mcg” is an input to an assay preparation, not a body-weight field.

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol so a multi-use vial is less likely to become a culture after the first needle. It is the wrong solvent for some sequences, and benzyl alcohol is the wrong additive for some assays. A good lab note records which solvent was used and why. Matching solvent to method is part of the chemistry.

Mass, volume, and units are dilution math — nothing more mysterious than that.