How to Read a Research Peptide COA

A Certificate of Analysis (COA) is a lot-specific quality document issued after a batch of peptide is synthesized and tested. It tells you three things: what is in the vial, how pure it is, and which physical lot the measurements came from. A COA is not a marketing sheet — every number should trace back to a raw instrument file that a lab can produce on request.

The COA is only meaningful for the exact lot number printed on it. A vendor who ships one product with a COA from a different lot has given you a decorative PDF, not documentation.

Every legitimate COA opens with the same block. Verify each field:

• Product / compound name — matches your order and the vial label exactly.
• Molecular formula & molecular weight — matches the published sequence.
• CAS number — when the compound has one.
• Lot / batch number — matches the number printed on the vial.
• Manufacture & retest / expiry dates — a peptide with no dates is a red flag.
• Appearance — usually "white to off-white lyophilized powder."
• Solubility — the solvent(s) the material was validated in.

Reversed-phase HPLC (RP-HPLC) separates the target peptide from truncations, deletions, oxidations, and racemized diastereomers. The COA reports purity as the area percentage of the target peak versus every other peak in the chromatogram.

What to look for on the chromatogram:

• Purity ≥ 98% is the standard baseline for research-grade material. 99%+ is common for well-run syntheses of short/medium sequences.
• A dominant, symmetrical main peak with a clean baseline before and after.
• Method details: column (typically C18), gradient (e.g. 5–65% ACN in 0.1% TFA over 20 min), flow rate, injection volume, detection wavelength (usually 214 or 220 nm).
• Retention time reported and consistent with previous lots of the same peptide.

A "purity" number without a chromatogram, method, or wavelength is a claim, not a measurement. Ask for the raw trace.

HPLC tells you how much is the target. Mass spectrometry tells you the target is actually the right molecule. ESI-MS or LC-MS measures mass-to-charge (m/z) for the ions the peptide forms and deconvolutes them to the neutral monoisotopic mass.

• Observed mass matches the theoretical monoisotopic mass within about ±0.5 Da for typical instruments (much tighter on high-res).
• Charge states for larger peptides — you should see the expected [M+H]⁺, [M+2H]²⁺, [M+3H]³⁺ ladder.
• No unexplained mass shifts of +16 (oxidation), +42 (acetylation), −18 (dehydration), or +80 (phosphorylation / sulfation) unless the product is intentionally modified.
• Deconvoluted spectrum attached or referenced, not just a single number claimed in text.

For peptides intended to touch cells or tissue in research use, endotoxin matters. Endotoxin (lipopolysaccharide from Gram-negative bacteria) triggers immune responses at very low concentrations and confounds experiments.

• LAL / kinetic chromogenic assay reported in EU/mg.
• Bioburden reported in CFU/g when applicable.
• Materials destined for cell culture typically target < 1 EU/mg or lower depending on the assay.

A lyophilized peptide is not 100% peptide by weight. Two other numbers determine how much actual peptide is in the vial:

• Water content — Karl Fischer titration, reported as % w/w. 3–8% is typical.
• Counter-ion content — TFA or acetate salt, reported as % w/w. Basic peptides can carry 5–20% counter-ion.
• Net peptide content — the actual peptide fraction after subtracting water and counter-ion. This is the number you should use for dose-response math, not the raw powder weight.

A COA that ignores water and counter-ion is fine for identification but incomplete for quantitative research.

Look for explicit guidance, not vague "keep cool" language:

• Lyophilized storage — typically −20 °C, desiccated, protected from light.
• Reconstituted storage — solvent, concentration, and stability window (e.g. 4 °C for 7 days, −80 °C for extended).
• Freeze-thaw — limit specified; most peptides tolerate few cycles.
• Retest / expiration — a real date, not "when we say so."

• No lot number, or a lot number that doesn't match the vial.
• Purity claim with no chromatogram, method, or wavelength.
• Mass "confirmed" with no spectrum attached.
• Generic PDF reused across multiple products (same date, same peaks, different name).
• No manufacture or expiry date.
• Missing analyst signature or lab identifier — a COA is a document of record, not a marketing asset.
• Purity below 95% sold as "premium" or "pharmaceutical grade."

Every lot we ship comes with a COA that meets this checklist. See our testing standards, browse the catalog, or review our research-use policy.