Peptide net content calculator
Theoretical net peptide content is the peptide’s share of an ideal dry salt’s mass. Divide peptide molecular weight by peptide-plus-counterion molecular weight, then multiply by 100. This counterion-only estimate does not measure a vial’s actual content or HPLC purity.
Estimate the counterion contribution
Use the molecular weight of the peptide without its counterions. The number of counterions is an assumption you supply; this tool does not infer it from the sequence.
Calculated in your browser. Inputs are not submitted by this tool. Need a sequence-based mass? Use the molecular mass calculator. Do not use this estimate to adjust an administered dose.
Method and sources
A counterion-only estimate for TFA or acetate salts, with the formula and assumptions shown alongside your result.
How to Use
Enter the peptide molecular weight without salt counterions, in g/mol. For this calculation the numerical value matches molecular mass expressed in Da.
Choose TFA or acetate. The approximate masses, 114 and 59 g/mol, follow the published AmbioPharm teaching model.
Supply the assumed whole number of counterions per peptide molecule. Do not infer this from a product name or HPLC purity.
Calculate, then copy the result together with its assumptions. Editing any input clears the previous result.
Formula
Theoretical net content (%) = peptide MW ÷ (peptide MW + counterion count × counterion MW) × 100Example
For a 1,000 g/mol peptide and two TFA counterions: 1,000 ÷ (1,000 + 2 × 114) × 100 = 81.43%. This is an idealized counterion-only estimate, not a measured sample result.
Frequently Asked Questions
Is net peptide content the same as HPLC purity?
No. HPLC peak-area purity concerns detected chromatographic signals. Net content describes a mass fraction and can be lower because of counterions, water or other materials.
Can this tell me whether a vial is underfilled?
No. The net peptide content calculator uses assumed composition, not a sample measurement. Investigating an underfilled vial requires a suitable quantitative assay, such as an amount reported in mg per vial, on the same basis as the label claim.
What does this model leave out?
The counterion-only model leaves out water, residual solvents, excipients, other peptides, mixed counterions and uncertain salt composition. Actual net peptide content requires appropriate analytical characterization.
Why use approximate counterion masses?
This reproduces the cited teaching model. It is not an exact molecular-formula calculation, and additional displayed decimal places do not improve the assumptions.