The Basic Formula
Concentration = Amount of peptide (mg) ÷ Volume of solvent (mL)
Rearranged: Volume needed (mL) = Amount of peptide (mg) ÷ Desired concentration (mg/mL)
This simple formula determines how much bacteriostatic water to add to your lyophilized peptide vial to achieve your target concentration.
Common Reconstitution Examples
5mg vial + 1mL BAC water = 5mg/mL (5000mcg/mL)
High concentration. Good for protocols requiring small volumes per measurement.
5mg vial + 2.5mL BAC water = 2mg/mL (2000mcg/mL)
Medium concentration. Balanced between precision and concentration.
5mg vial + 5mL BAC water = 1mg/mL (1000mcg/mL)
Lower concentration. Easier to measure small quantities accurately.
10mg vial + 2mL BAC water = 5mg/mL (5000mcg/mL)
Standard reconstitution for 10mg vials.
Choosing Your Concentration
The right concentration depends on your measurement equipment and protocol requirements. Higher concentrations mean smaller volumes per measurement, which requires more precise equipment (insulin syringes vs. standard syringes). Lower concentrations are more forgiving but dilute the peptide further.
As a general rule: if you need to measure quantities below 100mcg regularly, use a lower concentration. If your protocol calls for milligram-scale quantities, a higher concentration is more practical.
Units Conversion
1mg = 1000mcg (micrograms). When your protocol specifies micrograms, divide by 1000 to convert to milligrams, then use the concentration formula to determine the volume to draw.
Example: You need 250mcg from a 5mg/mL solution. 250mcg = 0.25mg. Volume = 0.25mg ÷ 5mg/mL = 0.05mL = 5 units on an insulin syringe (where 100 units = 1mL).
Tips for Accuracy
Always use a clean syringe to add the bacteriostatic water. Inject slowly down the inside wall of the vial. Gently swirl — never shake. Allow the peptide to dissolve fully before drawing any for use. If calculating volumes for the first time, double-check your math before proceeding.
