How to Read a Peptide Certificate of Analysis Line by Line

A certificate of analysis is only useful if you can interrogate it. This walkthrough decodes each field, flags the three most common falsification patterns, and shows what a genuine chromatogram looks like.

Almost every peptide supplier now advertises certificates of analysis. Far fewer publish documents that survive scrutiny. The gap exists because most buyers glance at a purity percentage and stop reading. This article walks the full document, field by field, so you can tell a real analytical record from a formatted spreadsheet.

Field one: the lot identifier

The lot identifier is the spine of the whole document. It should appear in three places that agree with each other: on the vial label, on the certificate header, and in the supplier's public batch register. If any two disagree, or if the register does not exist, everything below the header becomes unverifiable. We treat a mismatched lot number as an automatic quarantine event.

Field two: the HPLC chromatogram

Reversed-phase HPLC separates the target chain from truncated sequences, deletion products and synthesis by-products. The number that matters is the main peak's area as a percentage of total integrated area. But the number without the trace is meaningless — you want the plot.

• A single dominant peak with a clean, symmetrical shape. Heavy tailing suggests column interaction or a co-eluting impurity.
• A visible, labelled baseline. A chromatogram cropped so the baseline is off-frame is hiding something.
• Retention time stated and consistent with the stated method and gradient.
• Integration marks drawn on the plot, so you can see where the analyst chose to cut the peak.
• Total area accounted for. If the listed impurities plus the main peak do not approach 100%, ask why.

Field three: the mass spectrum

HPLC tells you how pure the sample is. It does not tell you what the sample is. Only mass spectrometry confirms identity. The deconvoluted mass on the certificate should match the theoretical average mass of the intact sequence to within the instrument's stated tolerance. A purity figure without an accompanying mass confirmation is a claim about a compound nobody has identified.

Field four: counterion and water content

This is the field most often omitted, and it has direct arithmetic consequences. Synthetic peptides are usually isolated as trifluoroacetate or acetate salts, and the salt plus residual water can account for a meaningful fraction of the mass in the vial. A vial labelled 10 mg that carries a heavy counterion load contains less peptide than a buyer assumes. A certificate that reports net peptide content alongside gross mass is a sign of a supplier that expects to be checked.

The three common falsification patterns

1. The recycled document: one genuine certificate reused across many lots, identified by an analysis date that never changes even as lot numbers do.
2. The synthetic image: a chromatogram drawn in a graphics tool rather than exported from an instrument, recognisable by unnaturally smooth baselines and axis labels that do not match the stated method.
3. The absent identity: a beautifully formatted HPLC page with no mass spectrometry section at all, which proves purity of an unnamed substance.

How we publish ours

New Zealand Peptides publishes the full analytical package for every lot on an open batch register — no email request, no account required. Each vial's printed lot number resolves to the chromatogram and mass spectrum for that exact synthesis run, with the analysis date visible. If a lot has not been tested, it is not listed for sale.

Verification questions researchers ask

Why Peptide certificate of analysis matters to research labs

New Zealand research teams evaluating peptide certificate of analysis face three recurring questions before any in-vitro work begins: is the compound what the label claims, will it remain stable across the planned experimental window, and does the supplier's documentation hold up to the standards a principal investigator will sign off on. The remainder of this article is structured around those three questions.

New Zealand Peptides supplies peptide certificate of analysis as a lyophilised research material packaged for transit at ambient temperatures and long-term storage at −20 °C. Every batch ships with a lot-specific certificate of analysis covering identity, purity, residual solvents and endotoxin where downstream cell culture work is anticipated.

Typical research applications

Across the published literature, peptide certificate of analysis appears most often in three workflow categories. Each has its own documentation profile and storage requirements, which is why a single supplier batch is frequently subdivided across multiple aliquots to limit freeze-thaw cycling.

• In-vitro receptor binding and signalling characterisation, where milligram-scale aliquots are reconstituted fresh on the day of assay.
• Pharmacokinetic and stability modelling, where reconstituted material is sampled at defined time-points and analysed by RP-HPLC.
• Comparative reference work, where peptide certificate of analysis is benchmarked against in-house standards or other published research compounds.

Reconstitution and handling reference

Lyophilised peptide certificate of analysis is reconstituted with sterile bacteriostatic water using slow, side-of-vial addition to avoid foaming. The vial is allowed to dissolve passively rather than being shaken; mechanical agitation accelerates aggregation in many peptide systems and complicates downstream analytical work. The table below summarises common reconstitution volumes used as documentation references.

Storage and stability envelope

Lyophilised peptide certificate of analysis is documented as stable for 24+ months at −20 °C protected from light. Once reconstituted, the published storage reference for most research peptides in this class is up to 30 days at 2–8 °C when handled aseptically; longer-term storage of reconstituted material is best achieved by single-use aliquoting at −80 °C to remove freeze-thaw variables from later analytical reads.

• Avoid storing reconstituted vials in the refrigerator door — temperature swings shorten usable life.
• Label aliquots with batch ID, reconstitution date and concentration so retrospective audit is straightforward.
• Do not refreeze previously thawed aliquots; integrate single-use volumes into the assay design from the outset.

Certificate of analysis — what to verify

Every New Zealand Peptides peptide certificate of analysis lot is dispatched with a certificate of analysis (COA) tied to the batch identifier printed on the vial. Reviewing the COA before the material enters the workflow is the single highest-leverage quality control step a research lab can perform.

• Batch / lot identifier and synthesis date — both must match the vial.
• RP-HPLC purity, typically ≥98% for research-grade peptide certificate of analysis.
• Mass-spectrometry identity confirmation (LC-MS or MALDI-TOF) within ±0.5 Da of the theoretical mass.
• Counterion identity and percent (acetate or trifluoroacetate are the most common).
• Bacterial endotoxin per the published analytical method, reported in EU/mg.
• Residual solvents and water content where the synthesis route makes them analytically meaningful.

Quality benchmarks New Zealand Peptides publishes

Frequently asked research questions

Further reading

Continue with the related New Zealand Peptides research references linked at the foot of this article, or browse the full research catalogue for the compound class profile, lab-results archive and laboratory documentation. For sourcing questions, the research team is available via the New Zealand Peptides contact page.