How to Read a Certificate of Analysis (COA)

A certificate of analysis is the single most useful document a research peptide can come with. It is also the easiest to misread. A COA that looks impressive at a glance can turn out to describe a different lot, omit the method, or report a number with nothing to compare it against. This guide walks through a typical peptide COA section by section and explains what each result actually tells you.

What a COA Is (and Isn’t)

A COA reports test results for one specific batch. Every result on it applies to the lot number printed on the document, and only to that lot. It is evidence about a batch, not a guarantee about a product line.

A COA is not a specification sheet. A specification states what a product should meet. A COA reports what a particular batch actually measured, ideally alongside the specification so you can see whether it passed.

Section 1: Header and Issuer

Look for:

• Name of the issuing laboratory or organization, with contact details
• Report or certificate number, which allows the issuer to confirm the document
• Date of analysis and date of issue

Why it matters. An identifiable issuer makes a COA verifiable. If the lab name, report number, or date is missing, you have no way to confirm that the testing happened as described.

Section 2: Product Identification

Look for:

• Compound name, ideally with sequence or structural description
• Lot or batch number
• Theoretical molecular weight or monoisotopic mass
• Quantity or fill amount per vial, where relevant

Check the lot number first. Compare it, character by character, with the lot printed on your vial. This is the most important check on the entire document.

For blends, check each component. A vial such as the Wolverine Blend contains more than one peptide. Its documentation should address each component, not just the blend as a whole.

Section 3: The Test Results Table

Most COAs present results in a table with four columns: test, method, specification (acceptance criterion), and result.

Test	What it tells you	Typical method
Appearance	Physical form and color	Visual inspection
Identity	Is this the right molecule?	Mass spectrometry (MS)
Purity	How much of the peptide material is the target?	Reversed-phase HPLC with UV detection
Water content	How much residual moisture is present?	Karl Fischer titration
Net peptide content	How much of the powder’s mass is peptide?	Amino acid analysis or nitrogen analysis
Counterion content	How much salt (e.g., TFA or acetate) is present?	Ion chromatography or similar

Not every COA includes every test. Identity and purity are the core. The others add useful context, especially if you need accurate concentrations.

Specification vs result

A result without a specification is hard to interpret. “Purity: 98.2%” is more meaningful next to “Specification: ≥ 98.0%” and a clear pass/fail statement.

Methods matter too. Regulators expect analytical methods to be shown fit for purpose. The ICH Q2(R2) guideline on validation of analytical procedures describes characteristics such as specificity, accuracy, precision, and range. Research-grade COAs are not held to drug-approval standards, but a stated method is still a sign of rigor.

Section 4: Reading the HPLC Chromatogram

A chromatogram is a plot of detector signal against time. The sample is separated on a column, and each component appears as a peak at its own retention time.

What to look for:

• One dominant main peak. This should be the target peptide.
• Small side peaks. These are typically related impurities, such as truncated or modified sequences from synthesis. D’Hondt and colleagues’ 2014 review in the Journal of Pharmaceutical and Biomedical Analysis catalogues the common types, including deletion sequences and incompletely deprotected products.
• An integration table. Each peak’s area as a percentage of the total. The main peak’s area percentage is the HPLC purity.
• Method conditions. Column type, mobile phases, gradient, flow rate, and detection wavelength. Without these, the chromatogram cannot be reproduced or compared.

Purity is method-dependent. The same sample can give different purity values under different conditions. That is why the method should be stated.

For a deeper explanation, see Peptide Purity: HPLC & Mass Spectrometry Explained.

Section 5: Reading the Mass Spectrometry Result

Mass spectrometry confirms identity. It measures the mass-to-charge ratio of ions and lets the analyst infer the molecular mass of the main component.

What to look for:

• Observed mass alongside theoretical mass. The two should agree within a stated tolerance.
• The spectrum itself, showing the main signal. Larger peptides often appear as several charge states (for example [M+2H]²⁺ and [M+3H]³⁺), which the analyst deconvolutes into a single mass.
• Consistency with the compound. A mass that matches a different sequence, or a result with no theoretical value, is a problem.

Identity and purity are separate. A correct mass shows the target molecule is present. It does not show how much of the sample it represents. You need HPLC for that.

Section 6: Purity vs Net Peptide Content

These are two different numbers. As JPT Peptide Technologies explains, peptides are commonly isolated as trifluoroacetate salts. HPLC purity describes the target peptide relative to other peptide material. Net peptide content describes how much of the total powder weight is peptide, after accounting for counterions and water.

Example. A lot could report HPLC purity of 98% and a net peptide content of 80%. Both can be accurate at once. The second number matters when you calculate concentrations, as shown in our reconstitution guide.

Section 7: Date and Authorization

Look for:

• Analysis date and, where given, a retest or expiry date
• Name or signature of the person authorizing the report

A very old analysis date relative to when you received the material is worth noting. Check storage history and retest dates where given.

Red Flags Checklist

• No lot number, or a lot number that does not match your vial
• No identifiable testing laboratory or contact details
• No date of analysis
• Purity reported with no chromatogram, method, or specification
• Mass result with no theoretical value, or a value that does not match the compound
• Identical chromatograms or spectra across different lots
• Signs of editing, such as mismatched fonts or misaligned text
• A COA for a different compound, strength, or sequence than the one you purchased

How regulators think about impurities. For context, FDA guidance on generic versions of certain synthetic peptide drugs (2021) says a proposed generic should not contain any new specified peptide-related impurity above 0.5% of the drug substance, and that such impurities should be characterized. RUO materials are not drugs and are not subject to that guidance. But it shows how seriously impurity profiles are treated in regulated settings.

How A&A Wellness Approaches Documentation

Our standard: 99% purity, lab tested in the USA. Every A&A Wellness product is guaranteed to meet 99% purity and is tested by laboratories in the United States. Our quality standards page covers sourcing, handling, and packaging.

If you have a question about a lot, contact us with the lot number printed on your vial.

Key Takeaways

• Match the COA’s lot number to your vial before anything else.
• Identity comes from mass spectrometry; purity comes from HPLC. You need both.
• Look for methods, specifications, a chromatogram, a spectrum, a date, and an identifiable issuer.
• Purity and net peptide content are different numbers, and both can be correct.

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