Conditions: Homopeptide · liraglutide.
The figures are clear enough; the question is what they mean and what they do not.
I can supply the numbers if the specifics change the answer.
What would I need in addition before this supported a decision?
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.
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.
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.
Trifluoroacetate effects in cell culture are documented and are the technical basis for salt exchange to acetate.
Absence of a counter-ion figure is an absent measurement rather than a low one.
Purity says nothing about counter-ion. They are unrelated measurements.
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Browse resultsAnswer 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.
To be exact about it, 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.
Ask for net peptide content. It folds water and counter-ion into one usable number.
Answering this needs the purification method, since a trifluoroacetic acid mobile phase leaves trifluoroacetate unless a deliberate exchange was performed.
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.
Concretely, 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.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Trifluoroacetate unless a deliberate exchange was done. Ask which.
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