Most writing about peptide purity argues from one certificate. One certificate tells you about one lot. The interesting questions — is this consistent, does the fill track the label, does purity drift between batches — need several, and they need to be lots you can actually look at.
We publish eleven PEP-RTA-3 certificates: nine for PEP-RTA-3 on its own across four vial sizes, and two for the reta/cagri blend. This post reads all of them together. Every number below is on a published PDF with a verification code.
The data
| Lot | Size | Certificate | Purity | Content found | Overfill | Retention time |
|---|---|---|---|---|---|---|
| RETA10-0803 | 10 mg | COA7580 | 99.83% | 10.61 mg | +6.1% | 11.778 |
| RETA20-0803 | 20 mg | COA7599 | 99.79% | 20.22 mg | +1.1% | 11.770 |
| RETA30-0803 | 30 mg | COA7619 | 99.83% | 30.94 mg | +3.1% | 11.777 |
| RETA60-0803 | 60 mg | COA7629 | 99.85% | 61.26 mg | +2.1% | 11.762 |
| RETA10-0616 | 10 mg | COA5627 | 99.8% | 10.49 mg | +4.9% | 11.077 |
| RETA20-0616 | 20 mg | COA5628 | 99.9% | 20.58 mg | +2.9% | 11.059 |
| RETA48-0616 | 48 mg | COA5633 | 99.9% | 48.16 mg | +0.3% | 11.065 |
| RT30-0528 | 30 mg | COA4858 | 99.9% | 30.84 mg | +2.8% | 11.044 |
| RT60-0528 | 60 mg | COA4857 | 99.9% | 60.79 mg | +1.3% | 11.050 |
And the two blend lots, which report each component separately:
| Lot | Certificate | Purity | PEP-RTA-3 | PEP-CAG-A | Retention times |
|---|---|---|---|---|---|
| RTCAG15-0803 | COA7594 | 99.70% | 12.59 mg | 2.61 mg | 11.268 / 11.783 |
| RTCAG15-0616 | COA5635 | 99.9% | 12.59 mg | 2.68 mg | 10.574 / 11.057 |
Every lot reports a confirmed mass of 4731.2 g/mol for PEP-RTA-3 (and 4409.1 for PEP-CAG-A in the blends), identity by LC-MS/MS, purity by RP-HPLC at 214 nm, endotoxin <0.05 EU/mL and heavy metals <0.01 ppm.
Finding 1: purity is tight, and the spread is small
Nine single-compound lots, purity from 99.79% to 99.9%. Including the blends, 99.70% to 99.9%. That is a spread of 0.2 percentage points across five months of production.
Two honest caveats on reading that as "consistent":
- Significant figures are not uniform. Four lots report two decimals (99.83, 99.79, 99.85, 99.70) and five report one (99.8, 99.9). A lot printed as "99.9" could be 99.85 to 99.94. The reporting precision changed between batches, so the apparent tightness is partly a rounding artefact.
- Area percent has a blind spot. 214 nm sees the peptide bond. Non-peptide material — salts, counter-ions, water — is poorly seen. These figures describe peptide-related impurities and are silent about the rest, which is the distinction in net peptide content versus purity.
Finding 2: every lot is overfilled, and that is the useful finding
This is the one worth acting on. All nine single-compound lots contain more peptide than the label claims — between +0.3% and +6.1%, averaging about +2.7%.
That is not a bonus and it is not sloppiness. Fill processes target above nominal so no vial is ever short. The consequence is that the label is the wrong number to calculate with.
Work it through on the largest case. Lot RETA10-0803 is sold as 10 mg and contains 10.61 mg.
- Reconstitute into 2 mL assuming the label: you believe you have 5.00 mg/mL.
- Reconstitute into 2 mL with the certificate: you actually have 5.31 mg/mL.
A 6.1% error, systematic, applied to every point in a concentration series and to every aliquot taken from it. It is larger than the pipetting error most people worry about, and unlike pipetting error it does not average out — it biases everything in one direction.
The fix costs nothing: read the content field and divide by that. Reconstituting PEP-RTA-3 sets the arithmetic out, and molarity versus milligrams covers why molar amounts matter more than mass for a compound of this size.
Note also that overfill does not scale with vial size. The 48 mg lot is +0.3% and the 10 mg lot is +6.1%. Small vials carry proportionally more overage, because a fixed absolute overfill is a larger fraction of a smaller target. So you cannot estimate it — you have to read it per lot.
Finding 3: retention time tracks the batch, not the molecule
Group the retention times by batch suffix and the pattern is unmistakable:
| Batch | Lots | Retention time | Spread within batch |
|---|---|---|---|
| 08-03 | four lots | 11.762 – 11.778 min | 0.016 min |
| 06-16 | three lots | 11.059 – 11.077 min | 0.018 min |
| 05-28 | two lots | 11.044 – 11.050 min | 0.006 min |
Within a batch, retention times agree to about one part in a thousand. Between the August batch and the June one they differ by 0.7 minutes — roughly 6%.
The compound did not change; the confirmed mass is 4731.2 on all of them. What changed is the analytical run: column age, gradient, temperature, instrument. Retention time is a property of the separation, not of the substance. It is excellent for confirming two vials were analysed together and useless for comparing material across laboratories. How to read an HPLC chromatogram covers what the trace does and does not encode.
Finding 4: identical safety values mean "under the floor"
Endotoxin reads <0.05 EU/mL on all eleven. Heavy metals read <0.01 ppm on all eleven.
Identical values across eleven lots are not a sign of eleven identical measurements. They are limit-of-quantitation values: the assay cannot resolve below that threshold, so every passing lot reports the same string. The correct reading is "every lot was below the limit", not "every lot was the same".
This is why a certificate reporting endotoxin as a precise non-zero number is sometimes more informative than one reporting <0.05 — it means the assay actually resolved something. Neither is a problem; they answer slightly different questions.
What eleven lots cannot tell you
Being straight about the limits of this dataset:
- One laboratory. All eleven were issued by Bioviridian Inc. Consistency within one lab's method is not the same as accuracy, and cross-checking needs a second laboratory — which is what getting a peptide independently tested is for.
- Five months. Three batch dates between late May and early August 2026. That is not a long-term stability picture.
- No stability data. These are release certificates. They describe material at the point of testing and say nothing about what it does over the following year.
- Fields that do not exist. No water content, residual solvents, counter-ion or expiry date appears on any of them, so none of this speaks to those.
Frequently asked questions
Is PEP-RTA-3 purity consistent between lots?
Across the eleven lots published here, purity by RP-HPLC at 214 nm ranges from 99.70% to 99.9% — a spread of 0.2 percentage points. Part of that apparent tightness is reporting precision, since some lots are printed to one decimal and some to two.
Why does every vial contain more than the label says?
Fill processes aim above nominal so no vial comes up short. Across these lots the overage runs from +0.3% to +6.1%. It is deliberate, it is reported on the certificate, and it means the label is not the figure to calculate with.
Does a bigger vial have proportionally more overfill?
No — the opposite, in this data. The 48 mg lot is +0.3% while the 10 mg lot is +6.1%, because a fixed absolute overage is a larger fraction of a smaller nominal amount. Read the content field per lot rather than assuming a percentage.
Why do retention times differ between lots of the same compound?
Because retention time depends on the column, gradient, temperature and instrument, not only on the molecule. Within one batch these lots agree to 0.02 minutes; between batches they differ by 0.7 minutes, while the confirmed mass stays at 4731.2 throughout.
Can I compare these numbers to another vendor's certificates?
Purity and content, cautiously — if the method and wavelength match. Retention time, no. And any comparison assumes both laboratories are competent, which a certificate asserts rather than proves.
All material referenced is supplied for laboratory research use only. It is not for human or animal consumption, and nothing in this analysis describes a use in people.
References
- Bioviridian Inc. Certificates of analysis COA7580, COA7599, COA7619, COA7629, COA5627, COA5628, COA5633, COA4857, COA4858, COA7594, COA5635. coa.html
- United States Pharmacopeia. <85> Bacterial Endotoxins Test. 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.
