The case in front of me: JEEP · retatrutide.
I can parse the result. I am less sure what it licenses me to conclude.
I have deliberately not looked at anyone else’s interpretation yet.
Which parts of this are informative and which are decoration?
Answer first: the counter-ion is part of the mass you paid for and none of the peptide you wanted, and it can run to several per cent or more.
Trifluoroacetate has documented biological effects at higher concentrations in cell culture, which is the technical reason acetate exchange exists rather than a marketing one.
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.
Ion chromatography and fluorine NMR are the accepted quantitative methods for trifluoroacetate, and neither is a chromatographic purity method.
Water plus counter-ion is why gross mass and peptide mass differ.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsThe short version: peptides are supplied as salts, the salt is real mass, and neither purity nor a chromatogram will tell you how much of it there is.
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.
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.
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.
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.
Counter-ion content scales with the number of basic residues, following directly from charge balance.
Count the basic residues and you can estimate the counter-ion load.
edited 26 Jun 2025 by triple_agonist_q — added the citation requested in comments
The relevant arithmetic is that gross mass equals peptide plus counter-ion plus water, and the certificate usually reports only the first indirectly.
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.
Absence of a counter-ion figure is an absent measurement rather than a low one.
Trifluoroacetate unless a deliberate exchange was done. Ask which.
Mechanically, a net-peptide-content figure already accounts for it, which is why net content is the number worth asking for.
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.
Net peptide content varies between lots as the process varies, so one figure does not characterise a supplier.
Ask for net peptide content. It folds water and counter-ion into one usable number.
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.