Concentration¶

Definition¶

Concentration is the amount of peptide dissolved in a given volume of solvent, typically expressed as mg/mL (mass concentration) or mM/mol (molar concentration).

Overview¶

Accurate concentration calculation is critical for reproducible research. After reconstitution, the peptide concentration depends on the amount of peptide in the vial and the volume of solvent added — but must account for peptide content (assay), not just fill weight.

Technical Explanation¶

Concentration Calculations:

Mass concentration: Concentration (mg/mL) = Peptide content (mg) / Volume (mL)

Molar concentration: Concentration (mM) = Mass (mg) / (MW × Volume)

Important Correction: The labeled vial weight (e.g., 5 mg) includes peptide + counter-ion + water. The actual peptide content is: Corrected mass = Fill weight × (Assay / 100)

Example: - Fill weight: 5 mg - Assay: 85% - Actual peptide content: 5 × 0.85 = 4.25 mg - Reconstitute with 1 mL → Concentration = 4.25 mg/mL (not 5 mg/mL)

Importance in Peptide Documentation¶

Using the uncorrected fill weight overestimates concentration and leads to dosing errors. The COA provides the assay value needed for accurate concentration calculations.

Frequently Asked Questions¶

Q: Why can't I just use the labeled vial weight? A: The labeled weight includes peptide, counter-ion, and residual water. Using it directly overestimates the actual peptide content. Always correct using the assay value from the COA.

Q: Should I use mg/mL or Molar when reporting peptide doses? A: Both are valid, but molar concentrations (mM/µM) are preferred in research because they account for molecular weight differences between peptides and enable direct comparison of molar ratios.