Most peptide certificates are screenshots of someone else's document. This is how Purity Labs reads a COA line by line — and the seven signals that get a batch rejected.
A certificate of analysis is the only document standing between a research budget and an unusable vial, yet in this industry it is routinely treated as decoration. Purity Labs rejects batches on certificate grounds several times a year, and almost never because the headline purity number is low — it is nearly always something further down the page. Here is how to read the whole document.
The header: identity before anything else
Start at the top and confirm four things: compound name, sequence, molecular formula and theoretical monoisotopic mass. If the sequence is absent, the document is a marketing sheet rather than a certificate. If the stated mass does not match the sequence, the certificate has been assembled from a template — which tells you everything about the rest of it.
The HPLC section: read the trace, not the number
A purity figure of 99.4% means nothing without the chromatogram behind it. Look for a single dominant peak with a symmetrical profile, a clearly labelled wavelength (214 nm is standard for peptide bonds, 280 nm only detects aromatic residues and will flatter almost any sample), a gradient description and a run time long enough for late-eluting impurities to appear. A trace that ends at eight minutes is hiding the interesting part.
- Detection wavelength stated and appropriate to the sequence.
- Integration table showing every peak above threshold, not just the main one.
- Retention time consistent between the trace image and the summary table.
- Injection date within a sensible window of the synthesis date.
Mass spectrometry: identity confirmation
HPLC tells you a sample is clean; mass spectrometry tells you it is the right molecule. Purity Labs requires LC-MS or MALDI-TOF confirmation within ±0.5 Da of theoretical mass on every lot. Watch for masses that are close but consistently offset — a repeatable +16 Da suggests oxidation, and a −18 Da offset often points to dehydration during handling.
Counterion: the number that quietly changes your concentration
Synthetic peptides ship as salts, most commonly acetate or trifluoroacetate, and the counterion can account for a meaningful share of vial mass. A certificate that omits counterion content leaves you unable to calculate true peptide content, which means every downstream concentration is an estimate. Purity Labs quantifies counterion by ion chromatography and states it.
| Parameter | Purity Labs requirement | Analytical method |
|---|---|---|
| Purity | ≥ 99% for release | RP-HPLC, UV 214 nm |
| Identity | ±0.5 Da of theoretical | LC-MS / MALDI-TOF |
| Counterion | Quantified and stated | Ion chromatography |
| Water content | Typically < 8% | Karl Fischer |
| Endotoxin | Reported per lot | LAL kinetic chromogenic |
Seven red flags that get a batch rejected
- No batch identifier, or one that does not match the vial label.
- A purity figure with no chromatogram attached.
- Chromatogram axes cropped out of the image.
- Analysis date preceding the stated synthesis date.
- Counterion omitted entirely.
- Laboratory name absent or unverifiable.
- The same certificate reused across multiple compounds with the header swapped.
Does Purity Labs test independently or rely on the manufacturer?
Both. Every lot arrives with manufacturer documentation and is then independently HPLC-MS verified before release, and the independent result is what we publish.
Where can I see certificates for current stock?
The Purity Labs lab-results register lists published certificates by batch identifier, linked from every product page.
What happens if a batch fails?
It is quarantined and never enters saleable inventory. We would rather show a compound as out of stock than release a lot below our published release floor.
