Net peptide content calculator.
A vial label states a gross mass of lyophilized powder. Peptide content says how much of that powder is peptide, and HPLC purity says how much of the peptide is the target sequence. Enter the three numbers to see where the milligrams go, and use the sequence section to estimate the counter-ion share for a given salt form. Runs in your browser; nothing is sent anywhere.
Gross mass to milligrams of peptide.
| Peptide material (all sequences) | - |
|---|---|
| Target peptide (content × purity) | - |
| Related impurities | - |
| Counter-ions and water | - |
Salt share from the sequence
| Molecular weight as that salt | - |
|---|---|
| Peptide share of the dry salt | - |
| In the gross mass above | - |
The salt estimate assumes one counter-ion per basic site and no water. Real powders hold less counter-ion than that ceiling and a few percent of water, which is why a measured content figure beats the estimate.
They multiply, they do not add.
Gross mass is the weight of everything in the vial: peptide, counter-ions, bound water and any other salts. Peptide content (also called net peptide content or peptide purity by weight) is the fraction of that powder which is peptide, measured by quantitative amino acid analysis, nitrogen determination or ultraviolet absorbance. HPLC purity is a different thing: the share of the peptide signal that belongs to the target sequence rather than deletion, truncation or oxidation products.
The target peptide in a vial is gross mass × content × purity. Ten milligrams at 85 percent content and 98.5 percent purity holds 8.37 mg of the sequence on the label. Quoting a 98.5 percent purity alone can suggest 9.85 mg, which overstates it by almost 18 percent. The purity vs content guide walks through the distinction.
Counter-ions and water.
Solid-phase synthesis cleaves and purifies peptides in trifluoroacetic acid, so the dried product is usually a trifluoroacetate (TFA) salt unless the maker exchanges it for acetate or chloride. Each protonated basic site, the free N-terminus plus lysine, arginine and histidine side chains, can carry one counter-ion. TFA weighs 114 g/mol, acetate 60 and chloride 36, so a short peptide with several basic residues can be 10 to 25 percent counter-ion by mass. The TFA vs acetate guide covers the exchange.
Lyophilized powders also hold water, typically a few percent, because the freeze-drying cycle leaves some bound and the powder adsorbs more from air once opened. Together the counter-ions and water explain why peptide content commonly lands between 70 and 90 percent. The salt section of the calculator gives the ceiling for the counter-ion share from the sequence; the measured content on a lab report gives the real figure.
A 10 mg vial, line by line.
| Gross mass on the label | 10.00 mg |
|---|---|
| Peptide content, 85 percent | 8.50 mg of peptide material |
| HPLC purity, 98.5 percent | 8.37 mg of the target sequence |
| Related impurities | 0.13 mg |
| Counter-ions and water | 1.50 mg |
| BPC-157 as a TFA salt (2 basic sites) | 1647.5 g/mol; 86.2 percent peptide at most, 13.8 percent TFA |
Content and purity figures are illustrative; a lab report gives the measured values for a specific lot. BPC-157 has one lysine and a free N-terminus, so two basic sites.
Measured mass on every report.
Helion's published lab reports state identity by mass spectrometry, HPLC purity and the measured mass of peptide in the vial against the labeled amount, so the figure you need is on the report rather than estimated. See the guide to reading a COA, the testing guide, the molarity calculator for turning milligrams into moles and the molecular weight calculator for any sequence.
Specs and storage by compound.
Questions (6)
What is net peptide content?
The fraction of a lyophilized powder that is peptide, by mass. The rest is counter-ions such as trifluoroacetate or acetate, bound water and other salts. It is measured by amino acid analysis, nitrogen determination or ultraviolet absorbance.
How is peptide content different from HPLC purity?
Content is peptide as a share of the whole powder. Purity is the target sequence as a share of the peptide. Milligrams of target peptide equal gross mass times content times purity.
Why is peptide content often only 70 to 90 percent?
Counter-ions from synthesis and purification, usually trifluoroacetate, plus a few percent of bound water make up the balance.
How many counter-ions does a peptide carry?
Up to one per basic site: the free N-terminus and each lysine, arginine and histidine. The calculator uses that ceiling; the real number is usually a little lower.
Does the salt form change the molecular weight?
Not the peptide's own molecular weight. It changes the weight of the salt and so the share of a powder that is peptide.
Where do I find measured content for a Helion lot?
On the lab report for that lot: the measured mass of peptide per vial sits beside HPLC purity and the mass-spectrometry identity result.
Published studies (4)
- Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides and Its Influence on Membrane Interactions
- Characterization of Synthetic Peptide Therapeutics Using Liquid Chromatography-Mass Spectrometry: Challenges, Solutions, Pitfalls, and Future Perspectives
- Synthetic pharmaceutical peptides characterization by chromatography principles and method development
- Sequence-specific determination of protein and peptide concentrations by absorbance at 205 nm
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.