A Certificate of Analysis is a single page that tells you whether the compound in your vial is what it claims to be. Most people skip it. Experienced researchers read it first.
The COA is not marketing material. It is a quality control document generated during or after synthesis, reporting the results of analytical testing performed on a specific batch of product. When it's done right, a COA gives you enough information to evaluate purity, identity, and suitability for your research. When it's done poorly, or fabricated, it gives you nothing. Learning to tell the difference is a skill worth having.
What a COA Should Contain
Not all COAs are created with the same rigor. At minimum, a legitimate COA for a research peptide should include:
Product identification. The peptide name, sequence (single-letter or three-letter amino acid code), catalog number, and batch/lot number. The batch number is critical. It ties this specific document to a specific production run. A COA without a batch number is a red flag.
Molecular weight. The expected molecular weight based on the amino acid sequence. This is a calculated value, and it should match the mass spectrometry result (see below). For BPC-157, you'd expect to see 1,419.53 Da. For TB-500 (full-length fragment 17-23), 840.97 Da. If the stated molecular weight doesn't match published values for the compound, something is wrong.
HPLC purity. This is the most referenced number on any COA, and it's the one most frequently misunderstood.
Understanding HPLC Purity
High-Performance Liquid Chromatography separates a sample into its component parts based on how they interact with a stationary phase under high pressure. The output is a chromatogram, a graph showing peaks at different retention times. The main peak represents your target peptide. Smaller peaks represent impurities: truncated sequences, deletion sequences, oxidized forms, residual reagents.
Purity is calculated as the percentage of the total peak area represented by the main peptide peak. A report of 98.5% purity means that 98.5% of the detected material is the intended peptide, and 1.5% is something else.
What to look for:
The chromatogram itself should be included or available upon request. A purity number without the underlying data is less meaningful. Look at the baseline. A clean baseline with a single sharp main peak indicates good synthesis. Multiple significant peaks suggest impurities. The retention time of the main peak should be consistent with the expected hydrophobicity of the peptide. Each amino acid sequence has a characteristic retention profile.
Purity thresholds for research:
Below 95%: generally unsuitable for controlled research. Impurity levels are high enough to introduce variables.
95-97%: acceptable for some applications, but impurities may affect sensitive assays.
98%+: the standard for quality research-grade peptides. Most reputable suppliers target this range.
99%+: pharmaceutical-grade. Unnecessary for most research applications but available for work requiring the highest precision.
Mass Spectrometry
If HPLC tells you how pure your sample is, mass spectrometry tells you what it is. Mass spec measures the mass-to-charge ratio of ions derived from your sample. For peptides, this typically produces a molecular ion peak that should correspond to the expected molecular weight.
ESI-MS (Electrospray Ionization Mass Spectrometry) is the most common technique for peptide analysis. It generates multiply charged ions, so the raw data shows several peaks that, when deconvoluted, resolve to the expected molecular weight.
MALDI-TOF is another option, more commonly used for larger peptides and proteins.
On the COA, look for the observed molecular weight and compare it to the theoretical value. They should match within the instrument's margin of error (typically less than 0.1% deviation). A significant discrepancy suggests the wrong sequence was synthesized, or a modification (oxidation, deamidation) has occurred.
Amino Acid Analysis
Some COAs include amino acid analysis, which breaks the peptide down into its individual amino acids and quantifies them. This provides independent confirmation that the correct amino acids are present in the expected ratios. It doesn't confirm sequence order (mass spec and sequencing do that), but it catches composition errors.
This is a more expensive test and isn't always included. Its presence on a COA is generally a positive indicator of thorough quality control.
Endotoxin Testing
Endotoxins are lipopolysaccharides from gram-negative bacterial cell walls. They are potent immune stimulators and can confound in vivo research results by triggering inflammatory responses unrelated to the peptide being studied.
The standard test is the Limulus Amebocyte Lysate (LAL) assay, reported in endotoxin units per milligram (EU/mg). For research peptides:
Less than 5 EU/mg is generally acceptable. Less than 1 EU/mg is preferred for sensitive applications. For any in vivo animal study, endotoxin testing is not optional.
A COA that includes endotoxin testing demonstrates that the supplier understands what researchers actually need, not just what looks good on paper.
Appearance and Solubility
These are qualitative observations, but they matter. The COA should note the appearance of the lyophilized product (typically "white to off-white powder") and expected solubility in standard solvents. Deviations from expected appearance, such as discoloration or clumping, can indicate degradation or contamination during manufacturing.
Red Flags
No batch number. A COA without a lot or batch number cannot be tied to the specific product you received. It may be a generic template used across all batches.
No chromatogram. A purity number without supporting analytical data is an assertion, not evidence.
Purity claims above 99.9%. Achieving 99.9% peptide purity is extremely difficult and rare. Claims this high, especially from low-cost suppliers, should be viewed skeptically.
Inconsistent molecular weights. If the COA states a molecular weight that doesn't match published values for the peptide, the compound may be misidentified or incorrectly synthesized.
No third-party testing. In-house testing by the manufacturer is standard, but independent third-party verification from an accredited laboratory provides stronger assurance. Some suppliers offer both.
Identical COAs across batches. If you order the same peptide twice and receive COAs with identical data points (same purity to the decimal, same mass spec values), the documents may be fabricated or recycled from a previous batch. Batch-to-batch variation is normal. Identical results are suspicious.
What to Do With This Information
Read the COA before opening the vial. If the purity is below your threshold, the molecular weight doesn't match, or the document lacks critical information, contact the supplier before proceeding. Quality suppliers will provide additional documentation or replace the product.
Keep COAs on file for every batch used in your research. If results need to be audited or replicated, the COA establishes the quality of the material used. This is basic laboratory practice, but it's frequently neglected in peptide research.
The document is not a formality. It is the only objective evidence you have that the powder in your vial is what it's supposed to be.