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What a certificate of analysis (COA) should show — and red flags to look for

Published 17 Oct 2026 · By The QLD Analytical Team

Informational guide for research samples — not medical advice. QLD Analytical arranges independent testing; we do not sell or endorse any product.

What a COA is for

A certificate of analysis (COA), sometimes called a certificate of analysis or CofA, is the document that summarises quality-control results for one batch of material. For peptides, a serious COA should answer four practical questions for the specific vial or lot you are holding: Is it the compound named on the label? How clean does it look by the stated analytical method? How much active material is present relative to salts and moisture? And when, where, and on which sample was testing performed?

Peptide manufacturers with in-house QC typically report identity, purity, water, residual solvents, and counter-ions such as trifluoroacetate (TFA) or acetate, then summarise a selection of those results on the COA they ship to customers. That framework is described in Bachem’s peptide QC guide, which remains a useful reference even when you are reading a third-party or supplier document rather than a catalogue product.

Fields a peptide COA should include

At minimum, a COA you can rely on for research documentation should be tied to an identifiable batch. Look for a lot or batch number, a test or report date, the product name (sequence or INN-style name), and the analytical laboratory or issuer that stands behind the results. Without those anchors, the certificate cannot be matched to the vial in your hand or challenged if something looks wrong later.

The headline analytical lines most researchers expect on a peptide COA include:

• Identity — evidence that the material is the intended compound (for peptides, mass spectrometry and/or co-elution with a reference by analytical HPLC are common approaches).
• Purity — usually from analytical HPLC with UV detection around 210–220 nm, expressed as the main peak area as a percentage of the total peak areas in the chromatogram.
• Product content / net peptide content — on manufacturer COAs this is often a percentage that reflects peptide relative to non-peptidic material (counter-ions and moisture), measured with techniques such as Karl Fischer titration for water, gas chromatography for residual solvents, and ion chromatography or HPLC for acetate or TFA.

A strong COA also references or attaches the underlying data: chromatograms, spectra, or at least method identifiers so a knowledgeable reader knows what was done.

Methods behind the headline numbers

Identity and purity answer different questions. Identity testing asks whether the measured mass (and, where used, fragmentation pattern) matches the labelled sequence or formula. Purity by HPLC asks what share of detectable UV absorbance in the run belongs to the main peak assigned to your target — not whether every possible impurity is visible, because co-elution and method choice matter.

Bachem notes that analytical HPLC at 210–220 nm is the standard purity tool for peptides, with purity inferred from integrated peak areas. Separately, lyophilised peptides often retain water, residual solvents, and acid counter-ions bound to basic side chains (arginine, lysine, histidine). Those components are not measured by the same HPLC purity calculation, which is one reason manufacturers report both purity and net peptide content on fuller certificates.

When you compare COAs from different suppliers, check whether both documents used comparable methods and reporting rules. A percentage purity without a stated wavelength, column chemistry, or integration threshold is difficult to interpret across labs.

What QLD Analytical publishes

QLD Analytical is an independent intermediary: you send a labelled research sample, analysis is performed offsite by Apex Labs Pty Ltd, and we issue a certificate of analysis with a unique test number. Our standard mail-in panel covers identity by mass spectrometry, purity by HPLC, and net content for the vial — see how it works and pricing for what is included today.

On published results, each record shows fields you can use to verify a certificate, including test number, sample name, supplier or client name (unless you chose private or anonymous publication), batch or lot, sample received and tested dates, identity result, HPLC purity, and content (for example net amount in the vial compared with the label). Analysis is attributed to Apex Labs Pty Ltd, and the downloadable PDF includes the laboratory report pages, including chromatograms where provided.

For example, published record QA260926009 lists batch 146062026, tested 18 Aug 2026, identity confirmed, HPLC purity 99.1%, and content 8.5 mg for a 10 mg labelled sample — illustrating how identity, purity, and fill can be read together for one vial. That record applies only to that submission; it does not certify other lots or storage conditions.

Ordering an independent test does not validate a supplier’s marketing claims; it documents what was in the vial you posted on the test date. Extended panels such as blend quantification, endotoxin (LAL), and heavy metals are listed as coming soon — on enquiry on our pricing page and are not part of standard online checkout at the time of writing.

Red flags on supplier COAs

Researchers often receive a one-page PDF from a vendor. Treat the following as warning signs — not proof of fraud, but reasons to seek independent testing or ask sharper questions:

• No lot or batch number, or a batch number that does not match your vial label.
• No test date, or a date that predates the product’s stated manufacture without explanation.
• No named laboratory, or only a logo with no legal entity — you cannot verify who ran the analysis.
• No method description for purity or identity (for example “HPLC purity 99%” with no wavelength or technique).
• No supporting chromatogram or spectrum when you request full documentation — especially if purity is quoted to several decimal places.
• Results that cannot be verified — no QR code, test ID, or public record when the seller claims third-party testing.
• Generic certificates that look reused across unrelated products or concentrations.

If a COA is the only evidence of quality, posting a sample for the standard identity, purity, and content panel is one way to obtain a dated record tied to your vial. See order a test when you are ready.

Sources

• Bachem — Quality control of amino acids & peptides: a guide (identity, HPLC purity at 210–220 nm, water, solvents, TFA/acetate, COA summary).
• QLD Analytical — Published results, How it works, example record QA260926009.