How to verify a peptide certificate of analysis
Quality · 4 min read · Updated November 2, 2026
To verify a peptide certificate of analysis, first match its lot number to the one printed on your vial, character for character. Then check the expected mass against the sequence and the found mass against the expected. Finally, confirm the document with its issuer: for SCALE Performance, enter the certificate number and verification key at scale-performance.com/verify.
Does the certificate belong to your vial?
A certificate can be genuine and still be the wrong one. Compare its lot number with the vial label, every character, including prefixes, dashes and leading zeros. Then check the compound name, and the sequence if one is given, against the product you ordered. The dates should make sense too: the test date falls before the vial reached you, and any retest date comes after the test date.
Pull the certificate from its source rather than trusting a forwarded copy. The lot number printed on each SCALE Performance vial matches its certificate, and certificates can be searched at scale-performance.com/coa by lot number, compound, certificate number or CAS number. Searching with the lot number from your own vial is the most direct check.
How do you check the mass against the sequence?
Calculate the expected mass yourself from the sequence, with a peptide mass calculator or by adding residue masses plus one water (18.01 Da). For the invented decapeptide GAYSLKTEVR (C49H82N14O16), the monoisotopic mass is 1,122.60 Da and the average mass is 1,123.26 Da. The certificate's expected mass should equal one of these, and it should be clear which.
Then compare the found mass with the expected mass. For a peptide this size, routine LC-MS agrees with the calculated value to within a few tenths of a dalton, and high-resolution instruments to within a few thousandths. A gap that equals a known chemical difference points to a specific error rather than measurement scatter.
Which mass differences point to a problem?
Several offsets recur. A found mass 1.01 Da high often means the m/z of the protonated ion, [M+H]+, was reported as the neutral mass; 22.99 Da high suggests a sodium adduct, [M+Na]+, reported the same way. A difference of 0.98 Da matches a C-terminal amide versus a free acid, and 42.01 Da an N-terminal acetyl group, so check whether a modification on the label was left out of the calculation.
Others reflect chemistry in the sample: 15.99 Da high is oxidation, typically of methionine; 0.98 Da high can also be deamidation of asparagine or glutamine; 18.01 Da low is loss of water; 17.03 Da low is an N-terminal glutamine cyclized to pyroglutamate. An expected mass that matches neither the monoisotopic nor the average value for the stated sequence means the certificate was calculated for a different molecule, or calculated wrongly.
What are the red flags of a copied or edited certificate?
Copying shows up as sameness. Identical found mass, purity and chromatogram on certificates for different lots is the clearest sign: real lots rarely agree to the second decimal place of purity, and no two runs produce the same baseline noise. A lot number that appears on certificates for two different compounds is another.
Editing shows up as inconsistency. Look for figures in a different font, size or alignment from the text around them, a blurred or boxed patch behind a number, or a purity the chromatogram cannot support, such as 99.8% beside side peaks that are plainly a few percent of the main peak. Dates that run out of order are another tell.
Missing pieces count too. A certificate with no lot number, no method, no expected mass, or a purity figure with no chromatogram leaves little to check, whoever issued it.
How do you use the SCALE Performance verify tool?
Every SCALE Performance certificate carries a certificate number and a verification key. Enter both at scale-performance.com/verify; a successful check confirms that the certificate is genuine.
A key check cannot see changes made to a copy after it was issued, so finish by opening the same certificate from scale-performance.com/coa, by its certificate number or lot number, and comparing every field with the copy you hold: lot number, compound, expected and found mass, purity, test date and retest date. Any difference means your copy is not the record.
What does a genuine certificate not prove?
Verification confirms the document, and the document reports only what was tested. SCALE Performance certificates report the manufacturer's own in-house results, not an independent laboratory's, and only the tests actually run: identity by LC-MS and purity by RP-HPLC at 214 nm. Endotoxin, sterility, heavy-metal and contaminant panels are not part of standard lot release. A certificate also cannot describe how a vial has been stored since it left, which is why handling records belong in your notebook.
Questions
How can you tell if a peptide certificate of analysis is fake?
Check that the lot number matches your vial, that the expected mass matches the sequence, and that the purity figure agrees with the chromatogram. Then confirm the document with its issuer; for SCALE Performance certificates, enter the certificate number and verification key at scale-performance.com/verify.
Can a genuine certificate belong to a different vial?
Yes. A real certificate for another lot of the same compound says nothing about your vial, which is why the lot numbers must match exactly.
What mass should a peptide COA report?
The expected mass should equal the monoisotopic or average mass calculated from the sequence, including any terminal modifications. The found mass should agree with it within the instrument's tolerance, typically a few tenths of a dalton or better for small peptides.
Are SCALE Performance certificates from an independent lab?
No. They report the manufacturer's own in-house test results for each lot, not results from an independent third-party laboratory.