I have both a purity figure and a content figure, which is why the discrepancy is visible.
I understand the observation; what I do not understand is the mechanism behind it.
I have read the two review articles that come up first and both assert this without a citation to a primary source.
What is actually going on here, physically?
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.
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.
| 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 |
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.
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 BiochemUsing different standards for different samples is a recipe for systematic disagreement, which is why validation requires that the same standard be used for the entire series.
The single highest-value check is verifying that the standard's certificate specifies its purity and gives a traceable source.
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.
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.
I would not accept a standard that does not come with a certificate stating its purity.
Ask for the standard's purity when you buy it.
Certified reference materials from national metrology institutes carry a purity statement and a statement of traceability, and both matter.
A standard of uncertain purity used to measure an unknown sample produces a result whose uncertainty is larger than you will have estimated.
On the detail: 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.
Certified reference materials are available from national metrology institutes and carry full documentation of their purity and traceability.
The practical summary: use a standard of declared purity and verified traceability, and check that the certificate is current.
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.