Research Guides
How to Read a Certificate of Analysis for Research Peptides
Sep
A certificate of analysis (COA) is a batch specific laboratory record that confirms what a vial contains, how pure it is and what it was screened for.
To trust one, match the batch number to the vial, check that identity was confirmed by mass spectrometry, read the HPLC chromatogram behind the purity figure, and confirm who carried out the testing and when.
The certificate of analysis is the most useful document that comes with any research compound. It is also one of the most misunderstood. Many certificates in this market are generic, reused across batches or impossible to trace back to a laboratory. This guide walks through each part of a peptide COA so you can judge whether the material in front of you is fit for your work.
Scope: this article explains how analytical results are reported. It does not describe any effect of any compound, and all Master Biolabs material is supplied for laboratory research use only.
Why a certificate matters for reproducible work
An experiment is only as reliable as the reagents that go into it. If two batches of the same peptide differ in identity, purity or contaminant load, results from one study cannot be compared with the next. Good cell culture guidance treats reagent characterisation and documentation as core to reproducibility for exactly this reason.
A product name tells you what a supplier intends to sell. A batch record tells you what was actually measured in one production lot. Only the second one belongs in your lab notes.
The four things every peptide COA should report
Batch number
Ties the result to one production lot. It must match the number printed on the vial.
Identity
Confirms the molecule is the expected sequence, normally by LC-MS comparing observed mass with theoretical mass.
Purity
The share of the sample that is the target peptide, normally by RP-HPLC, shown with its chromatogram.
Contaminant screens
Results for substances that are not the peptide, such as endotoxin and heavy metals.
Reading the identity result
Identity answers a simple question: is this the peptide it claims to be? It is usually established by liquid chromatography with mass spectrometry (LC-MS). A good certificate reports two figures side by side:
- Theoretical mass, calculated from the amino acid sequence.
- Observed mass, measured from the sample itself.
The observed value should sit very close to the theoretical one. Be wary of a certificate that simply prints “conforms” with no numbers or spectrum behind it.
Reading the purity result
Purity is normally measured by reverse phase high performance liquid chromatography (RP-HPLC). The sample passes through a column, its components separate, and a detector records each one as a peak. The purity figure is the area of the main peak as a share of the total peak area.
- Look for the chromatogram, not just a percentage. You should see one dominant peak and any smaller related peaks.
- Look for method details such as column type and detection wavelength, so another laboratory could repeat the test.
- Remember that purity belongs to a lot. One batch result says nothing about the next batch of the same product.
Analytical methods used for results like these are expected to be validated for their purpose, which is the subject of the ICH Q2(R2) guideline listed in the sources below.
Reading the contaminant screens
Identity and purity describe the peptide. Contaminant screens describe everything else that might be present.
- Endotoxin: fragments of bacterial cell walls that can interfere with cell based assays. If your work involves cell culture, this result deserves close attention.
- Heavy metals: confirms elements such as lead, mercury, cadmium and arsenic sit below the reporting limits used by the testing laboratory. ICH Q3D sets out the established framework for elemental impurities.
Who tested it, and when
A trustworthy certificate names the laboratory that performed the analysis, gives a test date and is authorised by someone at that laboratory. The date should make sense against the batch. Independent analysis, by a laboratory the supplier does not own, removes an obvious conflict of interest.
Warning signs on any certificate
- No batch number, or one that does not match the vial
- A purity percentage with no chromatogram behind it
- The same chromatogram appearing on different batches or different peptides
- No testing laboratory named and no method described
- A test date that does not line up with the batch
- Identical round figures across every product in a range
How Master Biolabs publishes certificates
Every batch we supply is analysed by an independent laboratory using RP-HPLC purity analysis with LC-MS identity confirmation, plus an endotoxin screen and a heavy metal screen. The certificate is published against the batch number, so you can open it on our COA page before you order and check it again when the vial arrives. Our Quality and Testing page explains the process in more detail.
- Match the batch number on the certificate to the vial
- Identity should show observed and theoretical mass by LC-MS
- Purity should come with an RP-HPLC chromatogram and method details
- Contaminant screens should cover endotoxin and heavy metals
- The testing laboratory and test date should be named
- Every result belongs to one lot, never to a product name
Frequently asked questions
It is a laboratory record for one production batch that reports identity, purity and contaminant screen results, along with the method used and the laboratory that carried out the testing.
No. Purity is measured on a specific lot. Each new batch needs its own analysis and its own certificate.
HPLC shows how much of the sample is one main component. LC-MS confirms that the main component is the expected molecule. A sample can be very pure and still be the wrong peptide, so both results are needed.
Enter the batch number printed on your vial on our COA page. Certificates are published before the batch goes on sale.
- International Council for Harmonisation, 2023. ICH Q2(R2) Validation of Analytical Procedures. View source
- International Council for Harmonisation, 2022. ICH Q3D(R2) Guideline for Elemental Impurities. View source
- Pamies D, Leist M, Coecke S, et al., 2022. Guidance document on Good Cell and Tissue Culture Practice 2.0 (GCCP 2.0). ALTEX, 39(1), 30 to 70. DOI
All Master Biolabs products are supplied strictly for laboratory research use only. They are not medicines and are not for human or veterinary use. Please read our Research Use Policy before ordering.