What Is a Certificate of Analysis?
A Certificate of Analysis (COA) is a document issued by a testing laboratory that reports the quality characteristics of a specific batch of a chemical compound. For research peptides, the COA is the single most important document for verifying that what you received matches what you ordered — in identity, purity, and quality.
Yet many researchers accept COAs at face value without understanding what the data actually means, how to spot potential issues, or what a trustworthy COA looks like compared to a questionable one.
Key Components of a Peptide COA
1. Product Identification
The top of a COA should clearly identify:
- Product name: The peptide compound (e.g., BPC-157, Semaglutide)
- Molecular formula: Chemical formula (e.g., C₆₂H₉₈N₁₆O₂₂ for BPC-157 free acid)
- Molecular weight: Expected mass in Daltons (e.g., 1419.53 Da for BPC-157 acetate salt)
- CAS number: Chemical Abstracts Service registry number (e.g., 137525-51-0 for BPC-157)
- Amino acid sequence: The full sequence in single-letter or three-letter code
What to check: Verify that the molecular weight and sequence match published literature for the compound. Any discrepancy is a red flag.
2. Lot/Batch Number
A unique identifier linking this COA to a specific production batch. This is critical — a COA without a lot number, or with a lot number that does not match the one on your vial, provides no quality assurance for the product you actually received.
What to check: The lot number on the COA must match the lot number on your product vial. If your supplier does not put lot numbers on vials, or the numbers don't match, you have no way to verify the COA applies to your product.
3. HPLC Purity
High-Performance Liquid Chromatography measures the proportion of the desired peptide in the sample versus impurities. The result is expressed as a percentage.
- ≥99%: Research-grade. Minimal impurities. Suitable for quantitative research.
- 95-99%: Acceptable for many research applications. Higher impurity levels may affect results in sensitive assays.
- <95%: Below research-grade. Significant impurities may confound results.
What to check: Look for the actual percentage (e.g., 99.4%), not just "≥99%." A specific number indicates the lab actually measured purity; a rounded claim may be a specification rather than a measurement. Also look for the HPLC chromatogram — the graphical output showing the purity peak and any impurity peaks.
4. HPLC Chromatogram
The chromatogram is a graph showing peaks detected during HPLC analysis. Key features:
- Main peak: Should be tall, sharp, and well-resolved (clearly separated from neighboring peaks). This represents the target peptide.
- Baseline: Should be flat and stable. A noisy or drifting baseline suggests analytical issues.
- Impurity peaks: Small peaks near the main peak represent impurities — typically synthesis byproducts, truncated sequences, or deletion peptides.
- Retention time: The time at which the main peak elutes. This should be consistent with expected values for the compound under the stated HPLC conditions.
What to check: A trustworthy chromatogram shows one dominant peak with a flat baseline. Multiple large peaks, excessive noise, or poor peak resolution suggest quality issues or analytical problems.
5. Mass Spectrometry Data
Mass spectrometry (MS) confirms the molecular identity of the peptide by measuring its molecular weight. The mass spectrum shows peaks corresponding to the peptide's mass-to-charge ratio (m/z).
- Observed mass: The measured molecular weight
- Expected mass: The theoretical molecular weight based on the amino acid sequence
- Acceptable deviation: ±0.1% is typical for most mass spectrometry methods
What to check: The observed mass should match the expected mass within the acceptable deviation range. A significant discrepancy may indicate the wrong peptide, an incomplete synthesis, or a modification error.
Why mass spec matters: HPLC tells you how pure the sample is; mass spectrometry tells you what is in the sample. A compound could be 99.9% pure by HPLC — but if the mass is wrong, it's 99.9% pure of the wrong peptide. Both tests are necessary for complete quality verification.
6. Appearance and Physical Properties
COAs typically include:
- Appearance: Expected to be "white to off-white lyophilized powder" for most peptides
- Solubility: How well the peptide dissolves in standard solvents
- pH: Of the reconstituted solution
7. Testing Laboratory Information
A credible COA identifies:
- Lab name: The laboratory that performed the testing
- Test date: When the analysis was performed
- Analyst/reviewer: Who conducted or reviewed the analysis
- Lab certifications: ISO 17025 accreditation or equivalent
What to check: The testing lab should be independent — not owned or operated by the peptide supplier. In-house testing presents a conflict of interest. The best COAs come from third-party labs with relevant accreditations.
How to Spot a Questionable COA
Not all COAs are equally trustworthy. Watch for these warning signs:
- No lot number: A COA without a batch/lot number cannot be linked to your specific product.
- Rounded purity claims: "≥99%" as the only purity statement (no specific measured value) may indicate a specification, not a measurement.
- No chromatogram: A purity claim without the supporting HPLC chromatogram cannot be verified.
- No mass spec data: HPLC alone confirms purity but not identity. Without mass spec, you cannot verify the correct peptide was synthesized.
- Generic formatting: COAs that look identical across different compounds and batches may be templates rather than actual test reports.
- No lab identification: If you cannot determine which lab performed the testing, you cannot verify the COA's authenticity.
- Old test dates: A COA dated years before your purchase may not reflect the current condition of the product.
- Missing test conditions: HPLC results should include the column type, mobile phase composition, flow rate, and detection wavelength. Without these, the analysis is not reproducible.
What a Best-in-Class COA Looks Like
BeaCapra COAs are designed to meet the highest transparency standards:
- Specific measured purity percentage (e.g., 99.4%, not "≥99%")
- Full HPLC chromatogram with labeled peaks
- Mass spectrometry data with observed vs. expected molecular weight
- Batch-specific lot number matching the product vial
- Independent third-party lab identification
- Test date and analyst information
- Amino acid sequence verification
- Available on the product page before purchase
This level of documentation is the standard that every peptide supplier should meet — and that researchers should demand.
Using COAs in Your Research
Beyond quality verification, COA data serves several practical research purposes:
- Reproducibility: Recording the lot number and purity in your lab notebook allows other researchers to request the same batch or understand purity-related variability
- Dose accuracy: If purity is 98% rather than 100%, you may need to adjust your weighed amounts to achieve the correct active compound concentration
- Publication support: Many journals now require peptide source, purity, and testing documentation in the methods section
- Troubleshooting: If results are inconsistent between experiments, comparing COAs from different batches can identify quality as a variable
Frequently Asked Questions
Should I ask for a COA before purchasing?
Yes. A reputable supplier should provide batch-specific COAs proactively. BeaCapra publishes COAs directly on each product page, accessible before purchase. If a supplier cannot or will not provide a COA before you buy, consider that a warning sign.
What is the most important number on a COA?
HPLC purity percentage is the most cited metric, but mass spectrometry molecular weight confirmation is equally important. Purity tells you how clean the sample is; mass spec tells you what the sample actually is. You need both.
What does "third-party tested" mean?
Third-party testing means the analysis was performed by a laboratory that is independent of the peptide supplier. This eliminates the conflict of interest inherent in in-house testing, where the company selling the product is also the one certifying its quality.
How often should I check the COA?
Check the COA for every batch you receive. Even from the same supplier, different production batches can have different purity levels. When subscribing through BeaCapra, each delivery includes the COA for the specific batch shipped.
Can I request additional testing?
Most suppliers will provide additional testing data upon request. If the standard COA does not include mass spectrometry, endotoxin testing, or amino acid analysis, ask specifically. The willingness to provide additional data is itself a signal of quality confidence.