- A COA should be batch-specific and traceable to the label and supporting analytical files.
- HPLC purity, MS identity and peptide content are complementary results, not substitutes.
- Method conditions and acceptance criteria should be visible enough to interpret the reported number.
- A polished PDF without lot linkage or raw evidence is not a strong quality package.
Start with traceability, not the purity percentage
Before reading analytical results, confirm that the product name or sequence, lot number, manufacture or test date and container label agree. The COA should identify the material actually supplied. A generic specification sheet can describe expected limits, but it is not a substitute for a batch-specific release document.
For catalog materials, match the COA SKU and lot to the commercial record. For custom synthesis, verify sequence direction, N- and C-terminal states, modifications, salt form and requested quantity basis. Any ambiguity at this stage can make otherwise correct analytical data irrelevant.
HPLC purity: inspect the method and chromatogram
The COA should state the chromatographic method or enough conditions to understand the result: column type, mobile phases, gradient, detection wavelength and integration approach. The reported purity is normally target-peak area divided by total integrated area. It does not establish absolute peptide content.
When the project risk is high, request the chromatogram rather than relying on one number. Check that the target peak is identified, the baseline is credible, the run window is adequate and minor peaks have not been excluded without explanation. Closely related deletion, oxidation or epimeric species may require LC-MS or another orthogonal method [1].
Mass spectrometry: identity needs context
Mass spectrometry supports molecular identity by comparing observed ions with the expected molecular mass. Because peptides often appear in multiple charge states, the raw spectrum may show several peaks belonging to the same molecule. A useful report identifies the calculated mass, observed mass and assignment method.
A matching molecular ion is strong identity evidence, but it does not by itself prove purity, sequence order or concentration. Isobaric substitutions, stereoisomers and some co-eluting variants can require higher-resolution or orthogonal characterization. Regulatory and industrial literature therefore treats identity, purity and strength as separate quality attributes [2].
Content, water, counter-ion and other mass balance items
Peptide content is the fraction of the material attributable to the peptide rather than water, counter-ion and salts. It may be assigned by amino acid analysis, nitrogen analysis, quantitative NMR or a validated mass-balance approach. The appropriate method depends on the material and intended use.
For moisture-sensitive projects, water testing can explain differences between gross vial mass and active peptide mass. Counter-ion reporting matters because TFA, acetate and chloride affect molecular weight, solubility and experimental comparability. Residual solvents, elemental impurities, bioburden or endotoxin should be added only when relevant to the agreed research and supply specification.
COA red flags and a practical approval checklist
Red flags include a missing lot number, inconsistent product naming, impossible dates, a purity result with no method, identical chromatograms reused across lots, cropped axes, unexplained manual integration and a mass spectrum without calculated or observed values.
Before release, confirm five things: correct material, correct lot, passed acceptance criteria, supporting files available and storage/shipping requirements aligned. PeptideSum's COA library and technical documentation pages are designed to keep catalog identity, lot documentation and buyer review connected.
This article is for laboratory, analytical, procurement and qualified cosmetic-science contexts. It is not medical advice and does not provide dosing, administration or personal-use instructions.
Frequently asked questions
What should a peptide COA include?+
At minimum: material identity, lot number, test date, specification, result, release status, HPLC purity, MS identity and storage information. Content, water, counter-ion and other tests should be included when specified.
Can a mass spectrum prove 99% purity?+
No. MS supports identity and impurity characterization. A validated chromatographic method is normally used to report relative purity.
Should every peptide have endotoxin testing?+
Not automatically. The analytical package should match the research application and agreed risk controls. Endotoxin testing is not implied by HPLC purity and must be specifically requested when relevant.
Why ask for raw HPLC and MS files?+
They allow technical reviewers to inspect integration, peak shape, charge-state assignment and whether the summary COA accurately represents the underlying data.