First verify the amount of lyophilized peptide listed on the vial label. The label usually gives the total mass in milligrams and may include the peptide’s purity percentage. Record the molecular weight of the peptide, which you can find in the accompanying datasheet or literature. These three pieces of information - mass, purity and molecular weight - are the basis for all subsequent calculations.
Calculating mass concentration
Add the recommended volume of solvent using a calibrated pipette. For example, if the vial contains 10 mg of peptide and you add 1 mL of water, the nominal concentration is 10 mg/mL. If the peptide is 95 % pure, adjust the mass to reflect the actual peptide content: 10 mg × 0.95 = 9.5 mg. Divide this adjusted mass by the final volume to obtain the true mass concentration.
Converting to molarity
To express the concentration in molarity, divide the mass concentration by the molecular weight (in g/mol) and convert milligrams to grams. Using the previous example, 9.5 mg/mL is 0.0095 g/mL. If the peptide’s molecular weight is 1500 g/mol, the molarity is 0.0095 g/mL ÷ 1500 g/mol = 6.33 × 10⁻⁶ mol/mL, or 6.33 µM. Record the final value in your lab notebook for reproducibility.
Practical tips for accuracy
Practical tips: always use a calibrated pipette or syringe to measure the solvent volume, and verify the volume after addition if possible. Mix the solution gently by swirling; vigorous vortexing can introduce bubbles that affect volume measurements. If the peptide does not dissolve completely, allow the vial to sit at the recommended temperature for a few minutes and repeat gentle mixing. Once fully dissolved, store the solution according to the recommended temperature and light protection guidelines to maintain stability.
For research use only. This guide covers bench handling of laboratory research materials. It does not describe an application, benefit, dose, route or outcome, and nothing in it is guidance for use in a person or an animal. Nothing sold by PepXtide has been evaluated by the FDA.