Research Guides

How to Read a Peptide Certificate of Analysis (COA)

By the Nexaph team · Updated 6 November 2026 · 5 min read

A peptide certificate of analysis (COA) is the document that links one specific batch of material to the tests that were run on it. Read well, it tells you whether the molecule in the vial is the one on the label, how pure it is, and how much of the powder is actually peptide. Read badly, it is just a reassuring piece of paper. This guide walks through a typical peptide COA section by section and ends with a checklist of red flags.

What a peptide COA is, and what it is not

A COA reports results for a named batch, also called a lot. It is not a general product specification and it is not a promise that the material suits a particular experiment. Two kits of the same product from different batches should each have their own results, because synthesis and purification vary from run to run.

That is why the first thing to check on any peptide certificate of analysis is not the purity figure. It is whether the document belongs to the batch you actually hold.

The header: product, batch and dates

The top of a COA usually lists the product name, the sequence or structure, the molecular formula and theoretical molecular weight, the batch number, and one or more dates (manufacture, analysis, and sometimes a retest date).

• Batch number: it should match the batch printed on your label or the batch code on your order. At Nexaph, the SKU shown on each product page is the batch code for the current lot.
• Sequence and modifications: check that terminal modifications are stated. “Amidate” or “-NH2” means a C-terminal amide; “N-acetyl” or “Ac-” means an acetylated N-terminus.
• Dates: an analysis date years older than the batch, or identical dates on certificates for different batches, deserves a question.

Identity: does the molecule match?

Identity is normally confirmed by mass spectrometry (MS), typically electrospray (ESI) or MALDI. The COA should give the theoretical mass and the observed mass, and ideally include the spectrum itself. The two values should agree closely; a mismatch of a few daltons can mean a missing residue, an unexpected modification or the wrong compound.

Modifications matter here. A C-terminal amide is about 0.98 Da lighter than the corresponding free acid, so an amidated peptide such as Epitalon Amidate should not report the same theoretical mass as standard Epitalon. Checking that the theoretical mass reflects the stated modifications is a quick way to catch a copied or generic certificate.

Mass spectrometry confirms that the expected molecule is present. It does not, on its own, tell you how pure the sample is.

Purity: reading the HPLC result

Purity is usually measured by reversed-phase high-performance liquid chromatography (RP-HPLC) with UV detection, commonly around 214–220 nm where the peptide bond absorbs. The reported figure is the area of the main peak as a percentage of all detected peaks.

• Look for the chromatogram, not just a number. A single dominant peak with small, well-separated minor peaks is what a high purity figure should look like.
• Check that the method is described: column, mobile phases, gradient and detection wavelength.
• Be wary of figures such as “100.00%”. Real chromatograms almost always show some minor peaks.

HPLC purity describes the peptide relative to other UV-absorbing, peptide-related species, such as deletion sequences or oxidised forms. It does not account for water or salts. Our guide to peptide purity testing explains the difference in more detail.

Content: how much of the powder is peptide

Lyophilized peptides are rarely 100% peptide by weight. The powder also contains counter-ions left over from purification (often trifluoroacetate or acetate) and some residual water. Net peptide content is the fraction of the weight that is actually peptide, usually determined by amino acid analysis or nitrogen content.

Not every peptide certificate of analysis reports it. If yours does not, ask whether the amount stated on the label refers to gross powder weight or to net peptide, because the two can differ substantially.

Other tests you may see

• Appearance and solubility: a basic check that the powder looks and dissolves as expected.
• Water content: often by Karl Fischer titration.
• Counter-ion content: for example TFA or acetate levels.
• Endotoxin or sterility: only some suppliers test for these, and only for some products.

Absence of a test is not automatically a problem, but a peptide certificate of analysis should be clear about what was and was not measured.

Who performed the testing

A peptide certificate of analysis should name the laboratory, reference its methods and be signed or otherwise authorised. Some suppliers test in-house, some use independent laboratories, and some do both. For independent labs, accreditation to ISO/IEC 17025, the international standard for the competence of testing laboratories, is a useful indicator. Third-party peptide testing services also let researchers send a sample for independent analysis if they want a second opinion on a batch.

Red flags on a peptide certificate of analysis

• No batch number, or a batch number that does not match your label or order.
• A purity number with no chromatogram, or an identity claim with no mass value.
• An observed mass that does not match the theoretical mass for the stated sequence and modifications.
• The same certificate, with the same dates, supplied for different batches.
• Signs of editing, such as mismatched fonts, misaligned values or a lab name that cannot be traced.
• A supplier who cannot answer basic questions about the method or the lab.

How to request a COA from Nexaph

Email support@nexaphpeps.com with the product name and the SKU from its product page, for example BPC-157 10mg. Because the SKU is the batch code, it identifies exactly which lot you are asking about. For background on why documentation matters for research materials, see what “research use only” means.

Peptide certificate of analysis: quick checklist

• Batch number matches your vial, label or order
• Theoretical mass reflects the stated sequence and modifications
• Observed mass agrees with theoretical mass, with a spectrum attached
• HPLC purity is backed by a chromatogram and a described method
• Net peptide content is stated, or you know what the label amount refers to
• The testing laboratory is named and traceable

Further reading: D’Hondt et al., “Related impurities in peptide medicines“, Journal of Pharmaceutical and Biomedical Analysis, 2014. This guide is for laboratory research purposes and is not medical advice.