I have both a purity figure and a content figure, which is why the discrepancy is visible.
I can do the algebra. I am not confident about the conversion factors.
If there is a standard way to lay this out, I would rather learn that than invent one.
Can someone walk through the arithmetic step by step?
A reference standard is a material of known identity and established purity against which you compare everything else, and it is the foundation of quantitation.
A standard purchased from a supplier carries a certificate stating its purity, and that purity is your starting point for understanding your result.
System suitability for a standard includes that replicate measurements of the same standard give consistent results, and if they do not, something in the method or the instrument is wrong.
Certified reference materials are available from national metrology institutes and carry full documentation of their purity and traceability.
Do not use an in-house standard without independent verification of its purity.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsStart from the certificate on the standard itself, because that tells you the uncertainty in every result that uses that standard.
Storing a standard in a freezer is better than storing it at room temperature, but how much better depends on the chemical stability of the standard.
Put another way, using a standard that is older than its certificate validity window is using a material of unknown purity, which defeats the purpose of having a standard.
Ask for the standard's purity when you buy it.
edited 22 Jan 2026 by charge_state_3 — removed a claim I could not source
Specifically, the standard is not the sample, and the standard is not a stability indicator — it is a measurement baseline against which all inference depends.
A reference standard that has been opened and used many times is more exposed to contamination and moisture than a fresh standard is.
The relevant detail is that blank injections using only the mobile phase should give a clean baseline, and any peak in the blank is a contaminant that will affect your sample result.
The pharmacopoeial standards specify system suitability requirements for quantitative methods that include replicate injection agreement and that agreement should be tighter than two per cent.
The practical summary: use a standard of declared purity and verified traceability, and check that the certificate is current.
More usefully, a standard of low purity is worse than no standard at all, because low purity introduces a systematic error that is invisible without independent verification.
Comparing your quantitation result to a standard certificate requires that the sample purity be accounted for — if you measure a 95 per cent pure sample against a 99 per cent pure standard, the content result is biased.
Do not use an in-house standard without independent verification of its purity.
Worth being precise here: the cost of a certified standard is cheaper than the cost of one wrong conclusion based on an unverified standard, which is the argument for using them.
A standard of uncertain purity used to measure an unknown sample produces a result whose uncertainty is larger than you will have estimated.
Certified reference materials are available from national metrology institutes and carry full documentation of their purity and traceability.
Ask for the standard's purity when you buy 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.