Reference

Research peptide glossary

The analytical and handling vocabulary that appears on certificates of analysis and vendor listings, in plain language. Most of the terms below are the ones a buyer nods along to and then cannot check.

Analytical

Certificate of Analysis (COA): The lab report for one specific batch.; A document produced by an analytical laboratory reporting what testing was run on a single, identified batch and what the instruments returned. A COA is only meaningful when it names the batch or lot, names the laboratory, carries a date, and shows the underlying data rather than a summary figure. A PDF that shows a purity percentage and nothing else is marketing with a laboratory typeface.
HPLC purity: How much of the material is the peptide you asked for.; High-performance liquid chromatography separates a sample into its components and measures the relative area of each. Reported as a percentage, usually from a reverse-phase C18 column read at 220 nm. The number alone is not the evidence: the chromatogram is. A genuine report shows the trace, the retention time, and the integration, so you can see whether a 99% figure came from a clean single peak or from a wide peak with impurities tucked under its shoulder.
Mass spectrometry (ESI-MS): Confirms the material is the right molecule, not just a pure one.; Electrospray ionisation mass spectrometry measures molecular weight. It answers a different question from HPLC: purity tells you how much of one thing is present, mass spec tells you what that thing is. A report should show the observed mass against the theoretical mass for the sequence, within the instrument's stated tolerance. Purity without identity is a pure sample of something unverified.
Endotoxin / LAL testing: Bacterial contamination, reported in EU/mg.; The Limulus amebocyte lysate assay detects bacterial endotoxin, a heat-stable contaminant that survives sterile filtration and autoclaving. It is reported in endotoxin units per milligram (EU/mg). This is the single most frequently omitted panel in the research peptide market, because it is the one most likely to fail. A vendor who publishes HPLC and mass spec but never endotoxin has usually made a choice, not an oversight.
Residual solvents: What is left over from synthesis and purification.; Gas chromatography screens for solvents carried through from manufacturing, most commonly acetonitrile, and from purification, most commonly trifluoroacetic acid. Reported as parts per million or as a percentage by weight. Relevant because residual solvent displaces mass: a vial containing measurable TFA salt contains proportionally less peptide than the label implies.
TFA salt: The counter-ion most peptides arrive attached to.; Trifluoroacetic acid is used during reverse-phase purification and remains bound to the peptide as a salt unless it is deliberately exchanged. TFA content typically runs a few percent by mass. It matters for two reasons: it reduces the actual peptide content per stated milligram, and it is biologically active enough to interfere with sensitive in-vitro assays. Acetate-exchanged material is available and usually costs more.
Net peptide content: The peptide mass, after subtracting everything that is not peptide.; A 10 mg vial is 10 mg of lyophilised powder, not 10 mg of peptide. Water, counter-ion salt, and residual solvent all count toward that mass. Net peptide content, usually determined by amino acid analysis or nitrogen determination, states how much of the powder is the peptide itself. Two vials with identical HPLC purity can differ meaningfully in net content.

Handling

Lyophilised: Freeze-dried into a stable solid.; Freeze-drying removes water by sublimation under vacuum, leaving a solid cake or powder that is far more stable in storage than a solution. Lyophilised peptide is what ships. It is reconstituted with a diluent before use. A vial that arrives as a loose powder rather than an intact cake has usually been shaken in transit, which is cosmetic, or has absorbed moisture, which is not.
Reconstitution: Dissolving the lyophilised solid into a working solution.; Diluent is added slowly down the inner wall of the vial rather than directly onto the cake, and the vial is swirled rather than shaken. Concentration is a function of the volume added against the net peptide content, not against the label weight. Our reconstitution calculator handles the arithmetic.
Bacteriostatic water: Water with 0.9% benzyl alcohol as a preservative.; Sterile water containing benzyl alcohol, which inhibits bacterial growth and so allows a reconstituted vial to be accessed more than once. Distinct from sterile water for injection, which has no preservative and is single-use. Counterfeit diluent is a recurring problem in this market and is covered in our safety alerts.
Cold chain: Temperature control maintained from the laboratory to the recipient.; Some sequences degrade measurably at ambient temperature over days. Cold-chain handling means insulated packaging and coolant maintaining a temperature range for the whole transit, not an ice pack thrown in at dispatch. Lyophilised material is generally more forgiving than solution, which is why most peptides ship dry.

Sourcing

Batch / lot number: The identifier that ties a vial to a specific COA.; A synthesis run receives a batch identifier, and every analytical result belongs to that batch, not to the product line. This is what makes a COA checkable: a vial number should resolve to a dated certificate for that exact run. A vendor publishing one COA under a product name, with no batch traceability, is publishing a sample of their best day.
Research Use Only (RUO): Not for diagnostic, therapeutic, veterinary, or human use.; A regulatory classification for material intended solely for laboratory research. RUO material is not manufactured, tested, or released to the standards required for use in humans or animals, and is not approved by any regulator for such use. The designation is a statement about permitted use, not a comment on quality.
Third-party testing: Analysis by a laboratory with no stake in the result.; Testing commissioned from an independent analytical laboratory rather than performed by the manufacturer on itself. It is worth what the independence is worth: a named laboratory, a report you can trace to that laboratory, and a batch identifier that matches the vial in your hand. An unnamed lab on an unbranded template is a self-test with extra steps.

Now put it to work on an actual document.

The COA checklist walks the same terms in the order they appear on a real certificate, with the failure mode next to each one.

Open the COA checklist →Reconstitution calculator