A typical peptide test report answers three questions: is this the right compound, how much of it is there, and how pure is it? Those answers matter, but they are not the whole picture. Several properties that laboratories care about are measured with entirely separate methods, and a report only covers the tests that were actually requested.
What a standard report covers
- Identity, usually by mass spectrometry, confirms the molecule is the one named on the label.
- Content, reported in milligrams, shows how much peptide is in the vial.
- Purity, usually by HPLC, shows the share of the detected material that is the target peptide.
Our guide to HPLC and mass spectrometry explains how each of these is measured.
Sterility
Sterility testing checks whether living microorganisms are present. It is a microbiological test: a sample is incubated in growth media and watched for growth over a set period. HPLC and mass spectrometry cannot detect bacteria or fungi, so a high purity figure says nothing about sterility.
Endotoxins
Endotoxins are fragments of the outer membrane of certain bacteria. They can be present even when no living bacteria remain, which is why they are tested separately from sterility. The usual method is the LAL (Limulus amebocyte lysate) assay, which reports results in endotoxin units (EU). Endotoxins can interfere with cell-based experiments, so some laboratories specify an endotoxin limit for materials used in those assays.
Heavy metals and residual solvents
Peptide synthesis uses solvents and reagents, and trace metals can enter from equipment or raw materials. Measuring these needs dedicated techniques, such as gas chromatography for residual solvents and ICP-MS for metals. A peptide can be highly pure by HPLC and still contain residues these methods would find, because HPLC with a UV detector does not see them.
Why a single report has limits
Every report describes one sample on one day. It shows what was in that vial when it was tested, not how the material will change over time. Stability is a separate question that depends on storage conditions. Our guide to storing lyophilised peptides covers the basics.
How to read a report with this in mind
Start with the list of requested tests, then read the results. If a test is not listed, the report makes no claim about it. If your work needs sterility, endotoxin or residue data, ask a supplier whether that testing exists before you order rather than assuming it does. The Apex BioLabs test report library shows exactly which tests each product’s report includes, and our guide on how to read a peptide COA walks through each field. For anything not covered, contact us.
