A peptide Certificate of Analysis (COA) is the lab report that tells you what is actually in a vial: whether the peptide is the right molecule, how pure it is, and which lot was tested. This guide explains each section of a typical research peptide COA, including HPLC purity, mass spectrometry, net peptide content and endotoxin data, and the red flags that suggest a COA should not be trusted.
What a COA is, and why the lot number matters
A COA is issued for a specific production batch, called a lot. Peptide synthesis varies from batch to batch, so a COA only describes the lot it names. The first thing to check is that the lot number on the COA matches the lot number on your vial. A COA with no lot number, or one that is reused across many products and dates, tells you very little about the material in front of you.
Most research peptide COAs include the same core fields:
- Product name and sequence, written in three-letter or one-letter amino acid code
- Lot (batch) number and test date
- Theoretical molecular weight, calculated from the sequence
- HPLC purity, usually as a percentage with the chromatogram attached
- Mass spectrometry (MS) result, the observed mass compared with the theoretical mass
- Appearance, for example white lyophilized powder (GHK-Cu is blue)
- Testing laboratory, and whether testing was in-house or third-party
HPLC purity: how much of the sample is the target peptide
High-performance liquid chromatography (HPLC) separates the components of a sample as they pass through a column. Each component appears as a peak on a chart called a chromatogram. Purity is reported as the area of the main peak as a percentage of the total area of all detected peaks. A result of 98% means the target peak accounts for 98% of the detected signal.
For in vitro work, many researchers look for at least 98% HPLC purity; 95–97% may be acceptable for exploratory work if the impurities are disclosed. Two caveats matter:
- HPLC purity does not confirm identity. A closely related impurity, such as a truncated sequence or an oxidized methionine, can elute very close to the main peak.
- A purity figure without the chromatogram is hard to verify. A clean report shows one dominant peak with small, labeled impurity peaks.
Mass spectrometry: is it the right molecule?
Mass spectrometry measures the mass-to-charge ratio of the molecules in a sample and is how a COA confirms identity. The observed mass should match the theoretical mass calculated from the sequence, usually within about 0.1% for standard electrospray (ESI) instruments.
Peptides often carry more than one charge in ESI-MS, so the spectrum may show the molecule at a fraction of its full mass. For example, BPC-157 has a theoretical molecular weight of about 1419.5 g/mol; a doubly charged ion ([M+2H]2+) appears near m/z 710.8. A good COA states which ion was observed so the numbers can be checked against the sequence.
| Peptide | Sequence | Theoretical MW (approx.) |
|---|---|---|
| BPC-157 | GEPPPGKPADDAGLV | 1419.5 g/mol |
| Selank | TKPRPGP | 751.9 g/mol |
| Semax | MEHFPGP | 813.9 g/mol |
| DSIP | WAGGDASGE | 848.8 g/mol |
| GHK-Cu | GHK · Cu(II) | 401.9 g/mol |
Purity is not the same as peptide content
A lyophilized peptide powder is never 100% peptide by weight. It also contains residual water (commonly 5–15%) and counter-ions left over from synthesis and purification, usually trifluoroacetate (TFA) or acetate. Net peptide content is the percentage of the powder’s total mass that is actually peptide, and it is typically measured separately by amino acid analysis or nitrogen analysis.
This is why a vial can be 99% pure by HPLC and still contain less than its label weight of peptide. A 10 mg vial with 75% net peptide content holds about 7.5 mg of peptide. Some COAs report peptide content and counter-ion type, and researchers who need precise concentrations for their experiments should ask for both.
Endotoxin, moisture and other tests
- Endotoxin (LAL or rFC test): measures bacterial endotoxin, reported in EU/mg. HPLC and MS do not detect endotoxin, so it must be tested separately. It matters most for cell-based assays, where endotoxin can trigger unwanted responses.
- Moisture (Karl Fischer): water content of the powder, which affects peptide content calculations.
- Counter-ion content: the amount of TFA or acetate salt in the powder.
- Sterility vs. bioburden: a sterility test is a pass/fail compendial test; a bioburden count only measures how many microbes were found. They are not interchangeable.
COA red flags
- No lot number, or a lot number that doesn’t match the vial
- No testing laboratory named, or no indication of whether testing was in-house or third-party
- HPLC purity reported with no chromatogram
- No mass spectrometry result, or an observed mass that doesn’t match the sequence
- Purity reported as exactly 100%
- The same COA reused for different peptides, sizes or dates
- Test methods not named
Requesting a COA from LuLu Peptides
A Certificate of Analysis is available on request for every product we carry. Email Info@LuLuPeptide.com with the product name and we will send the COA for the lot you receive. You can browse all of our lyophilized research peptides in the shop and find answers about ordering and storage in our FAQ.
All LuLu Peptides products are sold for laboratory research use only. They are not approved by the FDA for human or veterinary use and are not for human consumption. This article is for educational purposes and does not constitute medical advice.
