What I am working with: 60 mg · mazdutide.
I have worked this out and I would like someone to find the error, because I suspect there is one.
My working so far, for the record, is below, and I am fairly sure the error is in the unit conversion rather than the algebra.
How many significant figures are actually justified here?
Content assay requires a reference standard of known purity and traceability, which is why it costs more than purity testing does.
For peptides at 214 nanometres the response is roughly proportional to the number of peptide bonds, so truncation impurities have lower response factors and overestimate content.
| Component | Typical share | Counted in purity? | Counted in content? |
|---|---|---|---|
| Target peptide | 88–94 % | Yes, as main peak | Yes |
| Related impurities | 1–3 % | Yes, as other peaks | No |
| Counter-ion (TFA or acetate) | 2–8 % | No | No |
| Residual water | 2–6 % | No | No |
| Bulking agent, if present | 0–40 % | No | No |
The purity of the reference standard is stated on its certificate, and your content figure is only as good as that purity certificate is.
The limitation is that a quantitative method is only as good as the standard it uses, and a cheap standard is a false economy.
If a supplier gives you content without the standard's purity, ask them to provide it.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsSpecifically, two measures of the same vial can agree on purity and disagree on content by a few per cent, which usually means the content assay used a different standard.
Running multiple independent aliquots of the same sample should give results that agree to within the method precision, which is usually one to three per cent.
Peak area for a standard of known weight produces a response factor — area per unit mass — which is then applied to the sample peak to infer sample mass.
The practical summary: if you are ordering from a new supplier, budget for content assay on the first lot.
The honest answer is that you cannot know for certain what you have without a content assay, and the purity number alone is not enough.
Water content and counter-ion content are part of the gross mass but not part of the content assay result, which is why the two do not sum to label claim.
Quantitation against a certified reference material assumes the sample and standard are treated identically through the analytical method, which is why the method for calibration matters as much as the method for measurement.
The relative standard deviation on replicate quantitations of a homogeneous sample should be below two per cent when the method is under control.
Ask for both the purity and the content, and do not accept purity alone.
The underlying point is that most research-grade certificates report purity without content, which is exactly backwards from what users actually need.
A content assay is always paired with a purity assay because purity tells you what fraction of the measured mass is the target and content tells you the total measured mass.
If a supplier gives you content without the standard's purity, ask them to provide it.
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.