20% off your first order · get your codeShips TuesdayFree shipping over $350Every lot third-party tested · COA on filePlain, unbranded lab-shipment packaging20% off your first order · get your codeShips TuesdayFree shipping over $350Every lot third-party tested · COA on filePlain, unbranded lab-shipment packaging

How to read a peptide COA

How to read a peptide COA

A certificate of analysis (COA) is the record that ties a vial to an independent purity and identity result. If you cannot match the lot on the label to a certificate, you do not have a verifiable reagent—you have a claim.

This guide explains what Brant reports, what the numbers mean, and what should make you pause. It is not a safety assessment and not advice for human use. For Brant’s methods page, see Third-Party Testing. Look up lots at Certificates of Analysis.

What a usable COA must include

At minimum, a research-peptide COA should show:

  1. Compound name matching the vial label
  2. Lot number matching the vial (and packing slip)
  3. Purity method and result (for Brant: RP-HPLC, UV at 220 nm)
  4. Identity method and result (for Brant: ESI-MS vs nominal molecular weight)
  5. Test date and the laboratory that performed the work
  6. Enough detail to see that the lab is independent—not the seller writing its own pass/fail

Brant lot numbers use the format BR-YYMM-NNNN, printed on the vial under the compound name. Enter that number on the certificates page to open the record for that exact lot.

HPLC purity: what the percentage is

Reverse-phase HPLC (RP-HPLC) separates the target peptide from synthesis-related impurities. Purity is reported as the target peak area as a percentage of total peak area at 220 nm—the wavelength where the peptide bond absorbs.

Brant’s release specification is a minimum of 99% by RP-HPLC. A lot that assays below specification is not released for sale.

What HPLC purity does not tell you

Peak-area purity is a measure of chromatographic homogeneity, not of absolute mass content. It does not by itself account for residual water, counter-ion, or solvent. That is why net peptide content and purity are different numbers when both are reported. Do not treat a purity percentage as “percent active drug for dosing”—these are laboratory reagents, not finished pharmaceuticals.

Mass spectrometry: identity, not “more purity”

Electrospray ionization mass spectrometry (ESI-MS) measures mass-to-charge and confirms the observed mass against the nominal molecular weight calculated from the sequence (or structure). That is how you distinguish the correct compound from a different one with a similar HPLC retention time.

On a Brant certificate and product page:

  • The observed mass (MS) and the nominal MW should agree within the instrument’s tolerance
  • MS answers “is this the right molecule?”
  • HPLC answers “how clean is the chromatographic profile?”

Both matter. A clean chromatogram of the wrong compound is still the wrong compound.

Lot match: the non-negotiable check

Before you accept a vial into inventory:

  1. Read the lot on the vial label
  2. Confirm the same lot on the packing slip
  3. Open the COA for that lot on Certificates of Analysis
  4. Confirm compound name, purity, and identity match what you ordered

If a supplier shows a “typical” COA with no lot, or a certificate that cannot be tied to your vial, treat that as unverified stock.

Endotoxin (when reported)

Where reported, bacterial endotoxin is measured by Limulus amebocyte lysate (LAL) assay and expressed in endotoxin units per milligram. It reflects Gram-negative bacterial contamination introduced during production or handling. It is not a substitute for identity or purity testing.

Red flags

Walk away—or demand documentation—when you see:

  • No lot number on the vial, or a lot that does not resolve to a certificate
  • Seller-only “in-house” purity with no independent lab named
  • Purity without method (“99% pure” with no HPLC/MS detail)
  • Identity skipped (HPLC only, no mass confirmation)
  • Generic PDF reused across products or dates that never change
  • Consumer drug branding or medical claims on a “research” listing
  • Pressure to buy before you can read the certificate

What third-party testing is not

An independent purity and identity result says the vial contains what the label says, at the stated purity, on the stated date. It is not a safety assessment, not an approval by any regulatory authority, and not evidence of suitability for any particular experiment. Fitness for a given in-vitro use is the researcher’s responsibility.

Related reading

Sold as laboratory reagents for in-vitro research use only (RUO). Not for human or veterinary use.