A certificate of analysis is a short document and most of it is testable. The problem is that the fields are terse, the methods are named rather than explained, and two of the numbers mean something other than what they look like.
This walks a real one: lot RETA10-0803, certificate COA7580, PEP-RTA-3 10 mg, issued 17 August 2026 by Bioviridian Inc. Every figure below is on that certificate, and the same structure appears on all eleven PEP-RTA-3 certificates we publish.
The header: two dates, one code
Three things sit above the results, and all three matter.
Sample received and COA issued bracket the analysis — 11 August and 17 August on this lot, six days apart. A certificate with no received date tells you when a document was produced but not when the material was examined, and those can be very far apart.
The verification code — COA7580 here — is the field that makes the rest of the document checkable. It resolves at the issuing laboratory, not at the vendor. A certificate you can only verify by asking the seller is a claim; one you can verify at the lab is evidence. This is the single most important field on the page, and it is the one most often missing.
Identity: a method, or it means nothing
Identity: PEP-RTA-3 — Confirmed via LC–MS/MS — Conforms
Two words carry the weight: LC-MS/MS. Liquid chromatography separates the sample, then tandem mass spectrometry measures the mass of what came off the column and fragments it to confirm the structure is consistent.
What makes this checkable is the mass. PEP-RTA-3's molecular weight is 4731.2 g/mol, and the certificate reports exactly that. An instrument does not see 4731.2 directly — it sees charge states. On this certificate's mass spectrum you can read the [M+3H]³⁺, [M+4H]⁴⁺ and [M+5H]⁵⁺ peaks, which is the normal signature for a peptide of this size.
An identity line without a method is not an identity test. "Identity: PEP-RTA-3 ✓" with nothing beside it records that someone wrote the name down.
Content: the number that is not the label
Content: 10.61 mg — HPLC quantitation — Conforms
The vial is sold as 10 mg. The certificate says 10.61 mg. That is not an error, and it is not generosity — it is the measured mass of peptide actually in the vial, and it is the figure your arithmetic should use.
This surprises people, so it is worth saying plainly: content is what was found, label is what was promised. Across our eleven PEP-RTA-3 lots the found value is above the label every time — 10.61 against 10, 20.22 against 20, 30.94 against 30, 61.26 against 60. What eleven certificates show looks at that pattern in full.
The consequence is arithmetic. Reconstitute a "10 mg" vial into 2 mL and assume 5.00 mg/mL and you are 6% low, because the vial held 10.61 mg and your actual concentration is 5.31 mg/mL. For a concentration-response series that error propagates through every point. Reconstituting PEP-RTA-3 works the numbers through.
Purity: area percent, and what it cannot see
Overall purity: 99.83% — RP-HPLC (214 nm) — Conforms
Reverse-phase HPLC separates the sample over time; a detector at 214 nm measures absorbance; purity is the main peak's area as a percentage of all peak area.
Two limits follow directly from that definition:
- It is a proportion, not an absolute. 99.83% means the main peak was 99.83% of what the detector saw — not that the vial is 99.83% PEP-RTA-3 by mass. Content answers the mass question; purity answers the proportion question. Net peptide content versus purity separates them properly.
- 214 nm sees the peptide bond. It is chosen because every peptide absorbs there. Things without a peptide bond — counter-ions, residual salts, water — are poorly seen or not seen at all. A high area percent is silent about them.
So 99.83% is a real and useful number about peptide-related impurities, and it is not a statement that the vial is 99.83% pure in any broader sense.
Endotoxin and heavy metals: limits, not measurements
Endotoxin: <0.05 EU/mL — USP <85> — Conforms Heavy metals: <0.01 ppm — USP <232> — Conforms
Both are reported as less-than values, and that is the correct way to report them. The assay has a limit of quantitation; below it, the honest statement is "below this threshold", not a number.
EU/mL is endotoxin units per millilitre. All eleven of our PEP-RTA-3 lots report <0.05 EU/mL, which is the assay floor rather than a per-lot measurement — identical values across lots mean every lot was under the limit, not that every lot was identical.
Retention time: identifies the run, not the compound
Retention time: 11.778 min
This is the one field people over-read. Retention time is how long the compound took to come off the column, and it depends on the column, the gradient, the temperature and the instrument — not only on the molecule.
The clustering in our own data makes this concrete:
| Batch | Lots | Retention time |
|---|---|---|
| 08-03 | RETA10, RETA20, RETA30, RETA60 | 11.762 – 11.778 min |
| 06-16 | RETA10, RETA20, RETA48 | 11.059 – 11.077 min |
| 05-28 | RT30, RT60 | 11.044 – 11.050 min |
Same compound, same laboratory, retention times 0.7 minutes apart between batches and within 0.02 minutes inside a batch. The number tracks the analytical run. Use it to confirm two vials were analysed together; do not use it to compare material across laboratories.
What this certificate does not carry
Worth stating, because people look for them: our certificates do not report water content or Karl Fischer, residual solvents, counter-ion identity, a retest date or an expiry date. Those are real tests; they are simply not on this document. A post or a seller describing a field the certificate does not have is describing a document they have not read.
Reading order
- Verification code — can you check it at the lab?
- Dates — when was the material received, not just when was the paper issued?
- Identity and method — is a method named, and does the mass match 4731.2?
- Content — what is the actual mass, and have you used it instead of the label?
- Purity and method — area percent at what wavelength?
- Endotoxin and heavy metals — below what limit?
- Retention time — which run was this, and does it match its batch siblings?
Frequently asked questions
Why does the certificate say 10.61 mg when the vial says 10 mg?
Because 10 mg is the nominal label and 10.61 mg is the mass that was measured. Fill processes aim above the label so the vial is never short. Use the measured figure in your calculations; it is the one that is true of the vial in front of you.
Is 99.83% purity good for PEP-RTA-3?
It is consistent with every PEP-RTA-3 lot we have published, which range from 99.70% to 99.9% by RP-HPLC at 214 nm. Whether it is sufficient depends entirely on the experiment — the number is a measurement, not a grade. Is 98% purity good for a peptide covers how to decide.
What does "<0.05 EU/mL" mean — is that zero?
No. It means the endotoxin assay did not detect anything at or above 0.05 endotoxin units per millilitre, which is the limit of the test. Below that threshold the assay cannot distinguish a small amount from none.
Can two vials with different retention times be the same compound?
Yes, routinely. Retention time depends on column and gradient conditions as much as on the molecule. Our own lots differ by 0.7 minutes between batches while sharing an identical confirmed mass of 4731.2.
Does a certificate prove the vial in my hand matches it?
It proves what the laboratory found in the sample it received from that lot. The link to your vial is the lot number — which is why the lot on the vial and the lot on the certificate must match, and why a certificate with no lot number is not evidence about any particular vial.
Everything described here concerns laboratory analysis of research reagents. The material is sold for research use only, not for human or animal use, and no certificate field describes a use in people.
References
- Bioviridian Inc. Certificate of analysis COA7580, PEP-RTA-3 10 mg, lot RETA10-0803, issued 17 August 2026. coa.html
- United States Pharmacopeia. <85> Bacterial Endotoxins Test. www.usp.org
- United States Pharmacopeia. <232> Elemental Impurities — Limits. www.usp.org
- PubChem, National Library of Medicine. CID 171390338; C221H342N46O68, 4731. pubchem.ncbi.nlm.nih.gov/compound/171390338
Every product mentioned is sold for laboratory research use only and is not for human or animal use. Nothing on this page describes or recommends use of the material sold here in humans or animals.
