Lumera Labs Journal · Standards thinking
Reading a peptide Certificate of Analysis: field by field
Published 2025-02-27 · Lumera Labs Editorial · Kelowna, BC
Short answer. A reference-grade peptide COA shows lot-specific results for: HPLC purity (≥ 99%), ESI-MS identity confirmation (within 0.5 Da), net peptide content (≥ 80% by AAA), residual TFA (< 1%), endotoxin (< 0.5 EU/mg), and water content (Karl Fischer, < 5%). Anything missing or vague should make you reject the lot.
Field 1: HPLC purity
Reverse-phase HPLC at 220 nm is the standard. Look for the main peak percentage — that's your purity number. Reference-grade is ≥ 99%; some difficult sequences cap at 97–98%. Anything below 95% is sub-spec for serious research. The chromatogram itself should be visible on the COA, not just the percentage — peaks shouldn't have shoulder artifacts that suggest co-eluting impurities.
Field 2: Mass spectrometry
ESI-MS confirmation should show the observed mass within 0.5 Da of the theoretical mass. For longer peptides (> 30 residues) the tolerance opens to 1.0 Da. Watch for +22 Da signatures (sodium adducts) — they're common but should be the sodium adduct of the correct mass, not the +Na adduct of a +22 Da side product.
Field 3: Net peptide content (AAA)
Amino acid analysis decomposes the peptide and quantifies each residue. Net peptide content = (peptide mass) ÷ (total mass), excluding counter-ion and water mass. Reference-grade is ≥ 80%. Lower values mean you're paying for water or salt rather than peptide. Critical for stoichiometric-dosing experiments.
Field 4: Residual TFA
Trifluoroacetic acid is the standard cleavage agent in Fmoc SPPS. Reference-grade material should report residual TFA < 1.0%. High TFA can affect cell-based assay readouts at common stock concentrations, and shifts solubility behavior at neutral pH. Some peptides are converted to acetate counter-ion post-synthesis; the COA should specify which counter-ion is present.
Field 5: Endotoxin (LAL)
For cell-based work, endotoxin matters more than purity. Reference-grade is < 0.5 EU/mg by LAL assay. Low-endotoxin grade (< 0.1 EU/mg) is for assays involving immune-cell lines or innate-immunity readouts.
Field 6: Water content (Karl Fischer)
Lyophilized peptides retain residual water. < 5% by Karl Fischer is the standard. Higher values mean the peptide is hygroscopic or the lyophilization cycle was incomplete; both compromise dose accuracy.
What's missing on a weak COA
- "Per-product" COAs (not per-lot) — a generic COA isn't worth the paper it's printed on.
- No chromatogram visible — just a number is not enough.
- No third-party verification — the supplier's own QC alone is a weaker signal than independent retest.
- No date — when was the lot tested? COAs from before the synthesis date are a red flag.
Lumera's per-lot Janoshik COAs sit at /lab-results/ with chromatograms, mass spectra, and signed certificates from the third-party lab.
Frequently asked questions
What HPLC purity is acceptable for research?
≥ 99% is reference-grade. ≥ 95% is acceptable for many in-vitro screens. Below 95% is sub-spec for any serious research.
Why does net peptide content matter?
It tells you what fraction of the vial weight is actual peptide vs counter-ion and water. For stoichiometric experiments, 80% net peptide vs 60% changes your effective concentration meaningfully.
What is a 'lot-specific' COA?
A COA tied to one specific synthesis batch with the lot number printed on the vial. A 'per-product' generic COA is not lot-specific and is a red flag.
Should I trust the supplier's own COA?
Trust but verify. Independent third-party retest (e.g., Janoshik Analytical for Lumera) gives a stronger signal than self-reported QC alone.
Where can I see Lumera's COAs?
All published lots are at /lab-results/ with chromatograms and mass spectra signed by Janoshik Analytical.
Disclaimer: All Lumera Labs products are supplied for laboratory research use only. They are not approved by Health Canada for human consumption, therapy, or diagnosis. See our research-use declaration for full terms.