TL;DR
A Certificate of Analysis (COA) summarizes laboratory test results for research peptides. Key sections include HPLC purity (typically reported as percentage), mass spectrometry confirmation of molecular weight, endotoxin quantification in EU/mg, and sterility testing outcomes. Researchers should verify that HPLC purity exceeds 95-98% for most studies, confirm the observed mass matches the theoretical value within 0.1%, and check endotoxin below 1 EU/mg for cell-based work.
How to Read a COA
Understanding how to read a COA is the first step when evaluating research-grade peptides. The document lists the compound name, lot number, test methods, acceptance criteria, and actual results. Begin by confirming the lot number matches your vial. Then examine each analytical parameter in order.
HPLC Purity Analysis
High-performance liquid chromatography (HPLC) remains the primary method for assessing peptide purity. The COA reports the main peak area as a percentage of total integrated peaks. Values of 97% or higher indicate minimal impurities. Compare the retention time against the reference standard and note any secondary peaks that may represent deletion sequences or oxidation products. Always request the full chromatogram for detailed peak identification.
Mass Spectrometry Verification
Mass data confirm the peptide's molecular identity. Look for the observed m/z value matching the calculated monoisotopic mass. Deviations greater than 1 Da suggest synthesis errors or modifications. Electrospray ionization (ESI) or MALDI-TOF results are common; both should be within instrument tolerance. This section often appears immediately after the HPLC data on a certificate of analysis peptides.
Endotoxin Testing Results
Endotoxin levels are expressed in endotoxin units per milligram (EU/mg). For most in-vitro research, values below 0.1 EU/mg are preferred. The COA lists the method (LAL or recombinant factor C) and the limit of detection. If the result is reported as "not detected," confirm the assay sensitivity to ensure it meets your experimental threshold.
Sterility Assessment
Sterility testing follows USP <71> or equivalent protocols. The COA states whether the sample passed or failed the 14-day incubation for bacterial and fungal growth. A "sterile" result indicates no growth under the tested conditions. Researchers working with cell cultures should prioritize lots with documented sterility testing even when the peptide is supplied as lyophilized powder.
Additional COA Parameters
Some certificates include residual solvent analysis, water content by Karl Fischer titration, and heavy metal screening. These values help assess overall lot quality. Compare results against your laboratory's internal specifications before use in experiments.
Common Interpretation Pitfalls
Avoid assuming higher purity always equals better performance; sequence-specific impurities can still affect assay outcomes. Cross-reference multiple COAs from the same supplier to identify batch-to-batch consistency. When in doubt, request raw data files for independent review.
Frequently Asked Questions
What HPLC purity percentage is acceptable for research peptides?
Most laboratory protocols accept HPLC purity of 95% or greater, with 98%+ preferred for quantitative assays.
How do I verify the correct mass on a peptide COA?
Compare the observed molecular weight to the theoretical monoisotopic mass; deviations should remain within 0.05-0.1%.
What endotoxin level is suitable for cell culture research?
Endotoxin below 0.1 EU/mg is generally recommended for mammalian cell work; always match the level to your specific assay sensitivity.
Does a sterile COA guarantee the peptide remains sterile after reconstitution?
Sterility is confirmed on the lyophilized material; proper aseptic technique during reconstitution is required to maintain sterility.
Explore Further
Browse our [research peptide catalog](/shop) and review third-party [lab reports & COAs](/lab-reports) for every batch.
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**Research use only.** The information above is provided for educational and laboratory research purposes only. The compounds discussed are not approved for human or veterinary use, diagnosis, treatment, or the prevention of any disease. Nothing here is medical advice.