The concentration of a reconstituted solution is set entirely by how much diluent you add to a known mass of peptide. Getting this relationship right is fundamental to reproducible measurement.
The basic relationship
Concentration equals mass divided by volume. If you add more diluent, concentration falls; add less and it rises. Choosing a convenient concentration up front makes later measurement easier and reduces pipetting error.
Measure the diluent precisely
Use a calibrated pipette or graduated syringe and record the exact volume added. An approximate volume produces an approximate concentration, which undermines every result derived from it.
Why aliquot
Every time a vial is opened and warmed it is stressed. Dividing a reconstituted solution into single-use aliquots means you thaw only what you need, sparing the rest from repeated freeze–thaw cycles.
Label everything
Each aliquot should carry the compound, concentration, lot number and date. Unlabelled tubes are a reproducibility hazard.
Research use only. This is laboratory measurement guidance, not dosing instruction.