Every reputable peptide vendor will provide a Certificate of Analysis with their products. But not every COA tells the same story, and some tell no honest story at all. Understanding what you are looking at is the first step toward making informed purchasing decisions.
What Is a COA?
A Certificate of Analysis is a document issued by a laboratory that summarizes the testing performed on a specific batch of a compound. For research peptides, a proper COA should confirm what the compound is, how pure it is, and whether it meets acceptable standards for research use.
The document typically accompanies each batch or lot number and should be specific to the product you received, not a generic template reused across multiple batches.
Key Sections of a COA
Product Identification
The top of the COA should clearly state the peptide name, catalog or product number, batch or lot number, and the date of manufacture or testing. If any of these fields are missing, that is your first warning sign.
Appearance and Physical Description
Most lyophilized peptides are described as a white to off-white powder. This section confirms the physical state of the product. While it seems basic, discrepancies here (such as describing a peptide as a clear liquid when it should be lyophilized) suggest the COA may have been copied from another product.
HPLC Purity
This is the most important number on the document. High-Performance Liquid Chromatography (HPLC) measures the percentage of the target compound relative to total detectable material in the sample. For research-grade peptides, you want to see purity above 98%. Values below 95% are generally considered substandard for most research applications.
The COA should specify the HPLC method used, including the column type, mobile phase, and detection wavelength. Without method details, the purity number cannot be independently verified or compared across vendors.
Mass Spectrometry (MS) / Identity Confirmation
Mass spec data confirms that the compound is actually what the label says it is. The COA should report the observed molecular weight and the expected (theoretical) molecular weight. These values should match within an acceptable margin, typically less than 1 dalton for most peptides.
This is critical because HPLC alone cannot confirm identity. A sample could be 99% pure but still be the wrong peptide entirely. Mass spec closes that gap.
Amino Acid Sequence
Some COAs include the full amino acid sequence of the peptide. This is helpful for verification purposes, especially for longer or more complex peptides where synthesis errors are more likely.
Endotoxin and Sterility Testing
Not all COAs include sterility data, but for peptides intended for injection-based research, endotoxin levels matter. The Limulus Amebocyte Lysate (LAL) test measures bacterial endotoxin content. Acceptable levels are typically below 0.5 EU/mg. If a vendor claims their product is "sterile" but provides no sterility testing data, treat that claim with skepticism.
Water Content
Karl Fischer titration measures residual moisture in lyophilized peptides. High water content can accelerate degradation. Typical acceptable values are below 8% for most peptides.
Red Flags to Watch For
No Batch or Lot Number
A COA without a batch number is essentially a generic document. There is no way to trace it back to your specific product. Legitimate labs assign unique identifiers to every batch they test.
Identical Numbers Across Products
If a vendor provides COAs for five different peptides and they all show 99.2% purity with identical retention times and mass spec values, something is wrong. Different peptides have different molecular weights, retention times, and purity profiles. Cookie-cutter numbers are a hallmark of fabricated documents.
No Lab Name or Accreditation
A legitimate COA identifies the testing laboratory. The best COAs come from third-party, ISO-accredited labs that have no financial relationship with the vendor. If the COA only says "in-house testing" with no lab details, the results carry significantly less weight.
Suspiciously Perfect Numbers
Real analytical chemistry produces real-world results. A purity of 99.87% is believable. A purity of exactly 99.00% across every batch raises questions. Analytical instruments measure to specific decimal places, and legitimate results reflect that precision.
Missing HPLC Chromatogram
The best COAs include the actual HPLC chromatogram, which is the graphical output showing the peaks detected during analysis. A clean chromatogram with a single dominant peak and minimal noise is what you want to see. If no chromatogram is provided, you are trusting a number without seeing the evidence behind it.
PDF Metadata Discrepancies
This is an advanced check, but examining the metadata of a COA PDF can reveal inconsistencies. If the creation date predates the batch date, or if the document was created in a consumer image editor rather than lab software, those are warning signs worth noting.
How PeptideWatchdog Evaluates COAs
Our testing methodology includes a COA accuracy component that measures the deviation between what a vendor claims on their COA and what our independent lab analysis actually finds. A vendor might claim 99% purity on their COA, but if our HPLC testing shows 96.5%, that 2.5% deviation gets factored into their overall score.
We also evaluate whether the COA includes all expected sections, uses a credible lab, and provides traceable batch information. This COA transparency score accounts for 15% of a vendor's total lab grade.
The Bottom Line
A COA is a starting point, not a finish line. It tells you what the vendor (or their lab) claims about the product. Independent verification, like the testing PeptideWatchdog performs, is what tells you whether those claims hold up. When evaluating a vendor, look at the COA critically. The quality of their documentation often reflects the quality of their operation.