How to read a peptide Certificate of Analysis

A Certificate of Analysis (COA) is the single most useful document a research supplier can give you. It records what was tested on a specific lot, which methods were used, and what the results were. Read properly, it tells you whether the material in your vial is what the label says it is, and how much of it is the compound you ordered.

This guide walks through the sections of a typical peptide COA and what each one actually proves.

1. Start with the header

Before looking at any numbers, check that the document belongs to your material:

• Lot or batch number must match the number printed on your vial. A COA for a different lot tells you nothing about yours.
• Compound name and sequence should match the product ordered, including any modifications.
• Test date and laboratory should be present, with the analyst or reviewer identified.

A generic COA with no lot number, or one that is reused across several batches, is the first red flag.

2. Identity: mass confirmation

Identity is usually confirmed by mass spectrometry (MS). The report compares the theoretical molecular weight of the sequence with the observed mass measured by the instrument. The two should agree within the tolerance of the method, typically a fraction of a dalton to around one dalton depending on the technique.

A matching mass confirms that the main component is the correct molecule. It does not tell you how pure the sample is.

3. Purity: the HPLC result

Purity is measured by high performance liquid chromatography (HPLC). The sample is separated on a column and a detector records each component as a peak over time. Two figures matter:

• Retention time is when the main peak appears. It should be consistent with the reference method for that compound.
• Purity percentage is the area of the main peak as a share of the total peak area. A result of 99% means 99% of the detected material at that wavelength is the target peptide.

Where possible, look at the chromatogram itself rather than just the number. A single sharp main peak with small, well separated minor peaks is what you want to see.

4. Net peptide content is a different number

Lyophilized peptides are not 100% peptide by weight. They also contain water and counter-ions, such as acetate or trifluoroacetate, left over from synthesis and purification. Net peptide content expresses how much of the total powder mass is the peptide itself.

This is why a lot can be 99% pure by HPLC and still have a net peptide content well below 100%. The two figures answer different questions, and a complete COA reports purity at minimum and ideally both.

5. Appearance and other tests

Many COAs also record appearance (for example, white lyophilized powder) and sometimes solubility, water content or endotoxin results. These are useful supporting data, but they do not replace identity and purity.

Red flags to watch for

• No lot number, or a lot number that does not match the vial
• A purity figure with no method stated
• No mass confirmation, so identity is never actually shown
• Round numbers with no chromatogram or spectrum available on request
• No laboratory name or test date

How TLC Renew handles COAs

Every TLC Renew lot is tested for identity and purity before release, and each COA is keyed to its batch number. You can look up the certificate for any vial using the lot number printed on the label, so the document you read always matches the material on your bench.

All TLC Renew products are sold for laboratory research use only. They are not drugs, foods, cosmetics or medical devices, and are not for human or animal use. Nothing in this article is medical advice or dosing guidance.