Stated plainly: ERP · a GLP-1 receptor agonist.
I have read the primary source rather than the summary, which has left me with more questions.
I understand the headline. I do not understand the footnotes, and the footnotes look important.
What can I legitimately conclude from this figure?
The relevant arithmetic is that gross mass equals peptide plus counter-ion plus water, and the certificate usually reports only the first indirectly.
Worked reconciliation: a 10 mg vial at four per cent water and eight per cent trifluoroacetate contains 10.0 × 0.88 = 8.8 mg of peptide, a twelve per cent shortfall against label with a perfectly clean purity figure.
| Test | Answers | Does NOT answer |
|---|---|---|
| RP-HPLC, area % | What fraction of detected material is the target | How much target is present |
| Quantified content | Milligrams of peptide per vial | What the impurities are |
| ESI-MS identity | Whether the molecular weight matches | Purity, or isomeric substitution |
| Peptide mapping | Sequence, localised to a fragment | Quantity |
| Karl Fischer | Water content of the solid | Solvent content |
| LAL endotoxin | Pyrogen load in EU/mg | Sterility |
| Sterility test | Growth in defined media over 14 days | Endotoxin, or bioburden count |
Concretely, the number of basic residues drives counter-ion load, because each protonated basic site pairs with one counter-ion. A sequence with several lysines and arginines carries proportionally more.
Counter-ion content scales with the number of basic residues, following directly from charge balance.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Count the basic residues and you can estimate the counter-ion load.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemThe honest answer is that most certificates are silent on it and that the number can be large enough to matter.
Acetate salts are produced by a deliberate ion exchange after purification. The exchange costs a processing step and is the reason acetate-form material is more expensive.
On the detail: a supplier who reports both water and counter-ion has given you everything needed to reconcile the vial, and on this site that is a very short list.
Net peptide content varies between lots as the process varies, so one figure does not characterise a supplier.
Water plus counter-ion is why gross mass and peptide mass differ.
To be exact about it, this is the other half of the reconciliation problem, alongside water content.
Net peptide content — the fraction of gross mass that is the peptide itself — is the figure that folds water and counter-ion together and is what you should ask for if you ask for anything.
Worth being precise here: trifluoroacetate has documented biological effects at higher concentrations in cell culture, which is the technical reason acetate exchange exists rather than a marketing one.
Trifluoroacetate effects in cell culture are documented and are the technical basis for salt exchange to acetate.
Purity says nothing about counter-ion. They are unrelated measurements.
The underlying point is that acetate is generally preferred to trifluoroacetate for biological work, which is why the exchange is done at all.
Peptides purified by reverse-phase chromatography with a trifluoroacetic acid mobile phase are isolated as trifluoroacetate salts. The trifluoroacetate content depends on the number of basic residues and can run from a few per cent to well over ten by mass on a heavily basic sequence.
Ion chromatography and fluorine NMR are the accepted quantitative methods for trifluoroacetate, and neither is a chromatographic purity method.
Ask for net peptide content. It folds water and counter-ion into one usable number.
edited 9 Dec 2025 by loss_on_drying — reworded for clarity after a comment
Start with which counter-ion the process produced, because trifluoroacetate from reverse-phase purification and acetate from a salt exchange behave differently and are quantified differently.
Quantification differs by ion: trifluoroacetate by ion chromatography or by fluorine nuclear magnetic resonance, acetate by ion chromatography or by capillary electrophoresis. Neither shows up on a UV chromatogram.
Peptides from reverse-phase purification with trifluoroacetic acid mobile phases are isolated as trifluoroacetate salts, which is standard synthesis practice.
Trifluoroacetate unless a deliberate exchange was done. Ask which.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.