How to read a peptide COA

01

Start with the header

The top of the report identifies what was tested:

• The product name and the lot (batch) number.
• The testing laboratory’s name, and whether it is independent of the seller.
• Test and report dates.
• A verification link or code, if the laboratory offers one.

Before anything else, confirm that the lot number matches the one printed on your vial. A COA for a different lot tells you nothing about yours.

02

Identity: is it the right molecule?

Identity is usually confirmed by mass spectrometry (MS), which measures the mass of the molecules in the sample. The report compares the observed mass with the theoretical mass calculated from the expected formula.

A match confirms that the expected molecule is present. It does not say how much of the sample that molecule makes up; that is the purity result.

Check the expected formula against a reference such as PubChem. Our compound articles list them, for example and .

03

Purity: how much of it is the right molecule?

Purity is usually measured by high-performance liquid chromatography (HPLC). The sample is separated into its components, which are detected by UV absorbance; purity is the main peak’s share of the total peak area, reported as a percentage.

The other peaks are related impurities. For synthetic peptides, a 2014 review lists sequences missing an amino acid (deletions) or carrying an extra one (insertions), incompletely removed protecting groups, and residues with flipped stereochemistry (racemization).

A 99% HPLC purity means 99% of the UV-detected material is the main peptide. It does not measure water, salts or anything else the detector cannot see.

Sources: [1] Journal of Pharmaceutical and Biomedical Analysis · 2014

04

Content: how much is actually in the vial?

Content, sometimes called quantity or net peptide content, is the amount of peptide measured in the vial, compared with the label. It is separate from purity: a sample can be very pure and still underfilled or overfilled.

Lyophilized peptides are usually salts. Counter-ions from purification, such as acetate or trifluoroacetate, stay with the peptide, and residual water adds weight too, so the powder weighs more than the peptide alone.

A 2024 test-purchase study shows why both numbers matter: vials from unlicensed sellers measured 7.7% to 14.4% purity while their content exceeded the label by 29% to 39%.

Sources: [2] Pharmaceutics · 2019 · [3] Journal of Medical Internet Research · 2024

05

Other results you may see

Some reports add further tests:

• Endotoxin, reported in endotoxin units per milligram (EU/mg).
• Sterility or microbial limits.
• Residual solvents and heavy metals.
• Appearance and solubility.

Not every COA includes these. When they appear, check the method and the limit each result is compared against.

Sources: [3] Journal of Medical Internet Research · 2024

06

Verify the report

Four steps, every time:

• Match the lot number on the vial to the report.
• Use the laboratory’s verification link, or contact the lab, to confirm the report is genuine.
• Check that the report date fits the lot you received.
• Keep the report with your lab records.

Prism Labs publishes every lot’s report on the Quality & Testing page. Choosing a supplier: where to buy peptides.