How to Read a Peptide Certificate of Analysis (COA)

A peptide certificate of analysis (COA) is the lab report for one batch of material. It tells you what the peptide is, how pure it is, who tested it, and when. Reading one well takes a few minutes and is one of the most useful checks a lab can run before an experiment. This guide walks through each field, the warning signs to look for, and how to tie a vial to its own COA.

What is a peptide certificate of analysis?

A peptide certificate of analysis is a batch-specific document that reports purity and identity test results for one lot of peptide.

A lot, or batch, is a quantity of material produced and purified together. Every vial from the same lot should share the same test results. The COA is how those results travel with the product. It links a physical vial to a set of measurements through the lot number.

A good COA is specific. It names the compound and its lot. It states the testing lab, the test date, and the methods used. It reports results as numbers, not as marketing claims. If any of these are missing, the document is weaker evidence than it appears.

Which fields should a peptide COA include?

A complete peptide COA includes the compound name, lot number, testing lab, test date, purity with its method, identity by mass spectrometry, and appearance.

• Compound name and sequence: the peptide tested, sometimes with its amino acid sequence and molecular formula.
• Lot number: the batch code. It must match the code on the vial label.
• Testing laboratory: the lab that ran the assays. An independent third-party lab gives an outside check.
• Test date: when the analysis was performed.
• Purity: a percentage with the method named, such as HPLC or UPLC.
• Identity: a mass spectrometry result, ideally with observed and expected mass.
• Appearance: a description of the material, usually a white lyophilized powder.

Some COAs also report endotoxin results, water content, or net peptide content. These add detail but do not replace purity and identity.

How do you read HPLC purity on a COA?

HPLC purity is the area of the main peak divided by the total area of all peaks, shown as a percentage.

High-performance liquid chromatography (HPLC) pushes a dissolved sample through a packed column. Different molecules travel at different speeds and leave the column at different times. A detector, usually ultraviolet, records each one as a peak on a chart called a chromatogram. UPLC, or ultra-performance liquid chromatography, works the same way at higher pressure with smaller particles, which gives sharper peaks.

On the chromatogram, the tall main peak is the target peptide. Small peaks around it are impurities, such as truncated or deletion sequences. A result of 99.5% means the main peak makes up 99.5% of the total detected signal. Look for a single dominant peak and a stated method. A purity number with no method behind it cannot be judged. HPLC purity is not the same as net peptide content: water and counterions such as TFA or acetate do not appear on the UV chromatogram, so a 99% pure lot can still be well under 100% peptide by weight.

What does mass spectrometry show on a peptide COA?

Mass spectrometry confirms identity by showing that the measured mass of the peptide matches the mass expected from its sequence.

Purity alone cannot prove identity. A sample can be 99% pure and still be the wrong molecule. Mass spectrometry measures the mass of the molecules in the sample. Each peptide sequence has a known theoretical mass, calculated from its amino acids.

A strong COA shows both numbers: the expected mass and the observed mass. They should agree closely. Peptides often appear as several charged forms, so a spectrum may show more than one peak that all point to the same molecular mass. A COA that says "conforms" with no values gives you less to check.

What are the red flags on a peptide COA?

The main red flags are a missing lot number, no named lab, a purity figure with no method, and the same COA reused across different lots.

• No lot number: the document cannot be tied to any specific vial.
• No testing lab: you cannot tell who produced the result or whether it was independent.
• Purity without a method: a bare percentage has no context.
• Generic or reused COA: identical results and dates across many lots suggest a template, not a test.
• No identity data: purity with no mass spectrometry leaves the molecule unconfirmed.
• Missing or odd dates: a test date long before the lot was produced is a mismatch.

One flag does not always mean a problem, but each one is worth a question to the supplier. A reputable supplier answers with specifics.

How do you match a vial to its COA?

Match the lot number printed on the vial label to the lot number on the certificate, then confirm the lot with the supplier.

Start with the label. On a Puritide vial, the lot number is printed next to a QR code. Read it carefully, since the letter O and the number 0 are easy to confuse. Then compare it with the lot on the COA that shipped with your order. They must be identical.

Next, check it against the supplier's records. Puritide's lot verification page accepts the lot number, or opens with it filled in when you scan the QR code. A match shows the compound, lot, measured purity, testing lab, and test date, with a link to the certificate when one is posted. If a lot does not verify, email support@puritideresearch.com with a photo of the vial.

What does a real Puritide COA look like?

A Puritide COA reports purity by a named method from an independent lab, tied to a single lot number.

The sample certificate shown on the Puritide homepage is for lot G3R30-260613. It was tested by Aminos Analytics, an independent lab, and reports purity of 99.86% by UPLC. That one record shows the key fields in action: lot, lab, method, and result. Every batch is tested by HPLC for purity and mass spectrometry for identity.

All posted certificates are listed in the certificates of analysis library, searchable by compound name or lot. For broader context on what research peptides are and how they are produced, see our guide to what research peptides are. For a full supplier checklist, read how to choose a research peptide supplier.

For research use only. Certificates of analysis describe analytical testing of research materials. They are not a statement of fitness for any non-research purpose, and no product is for human or veterinary use.