If you’re conducting in-vitro laboratory research with peptides, understanding how to read a Certificate of Analysis (COA) is one of the most important skills you can develop. A COA is your primary tool for verifying that the peptide you received matches what was ordered — in identity, purity, and quality.

In this guide, we’ll break down every section of a peptide COA, explain what the numbers mean, and highlight the red flags that should make you think twice before using a product in your research protocol.

What Is a Certificate of Analysis?

A Certificate of Analysis is a document provided by a peptide manufacturer or third-party testing laboratory that reports the results of quality control testing performed on a specific batch of peptide. Think of it as a peptide’s “report card.”

A proper COA typically includes:

  • Product identification (peptide name, sequence, molecular weight)
  • Purity analysis (usually via HPLC)
  • Identity confirmation (mass spectrometry)
  • Physical characteristics (appearance, solubility)
  • Batch/lot information
  • Testing date and laboratory details

Every reputable peptide supplier should provide a COA for each batch they sell. If a vendor cannot or will not provide a COA, that is an immediate red flag for any serious researcher.

Key Sections of a Peptide COA

Peptide Identity and Sequence

The top of most COAs lists the basic identification information:

  • Peptide name — The common or catalog name (e.g., BPC-157, TB-500)
  • Amino acid sequence — The one-letter or three-letter amino acid code for the full peptide chain
  • Molecular formula — The chemical formula (e.g., C₆₂H₉₈N₁₆O₂₂)
  • Molecular weight (MW) — The theoretical molecular weight in Daltons
  • Lot/batch number — A unique identifier for the specific production run

What to check: Verify that the amino acid sequence matches the known published sequence for the peptide you ordered. Even a single amino acid substitution creates a fundamentally different compound. Cross-reference against databases like PubChem or UniProt if you’re unsure.

HPLC Purity

High-Performance Liquid Chromatography (HPLC) is the gold standard method for assessing peptide purity. This is arguably the most important number on the entire COA.

HPLC works by separating the components of a sample as they pass through a column. The main peptide peak is measured against any impurity peaks, and the purity is expressed as a percentage.

Typical purity grades for research peptides:

Purity Grade HPLC Purity Typical Use
Crude < 70% Not suitable for most research
Desalted 70–80% Basic research applications
Standard 80–90% General in-vitro research
High Purity 90–95% Most laboratory protocols
Ultra-Pure 95–98% Sensitive research applications
Research Grade > 98% Precision in-vitro studies

What to look for:

  • Purity ≥ 98% is ideal for most in-vitro research protocols. This is what serious researchers should target. For a deeper dive into what these percentages mean in practice, see our guide to understanding peptide purity.
  • Purity between 95–98% is acceptable for many applications but may introduce more variability.
  • Purity below 95% means significant impurities are present — truncated sequences, deletion peptides, or synthesis byproducts.

A good COA will include the actual HPLC chromatogram — a graph showing the peaks. You should see one dominant peak (your peptide) with minimal smaller peaks (impurities). If the chromatogram shows multiple large peaks of similar size, the sample has serious purity issues regardless of what the stated percentage claims.

Mass Spectrometry (MS)

Mass spectrometry confirms the identity of the peptide by measuring its molecular weight. While HPLC tells you how pure the sample is, mass spec tells you what the sample actually is.

The two most common methods used for peptides are:

  • MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization – Time of Flight)
  • ESI-MS (Electrospray Ionization Mass Spectrometry)

What to check:

  • The observed molecular weight should closely match the theoretical molecular weight listed on the COA.
  • An acceptable deviation is typically ±1 Dalton for small peptides and ±0.1% for larger ones.
  • If the observed mass is off by more than this, it could indicate the wrong peptide, a modification, or degradation.

Example: If BPC-157 has a theoretical MW of 1419.53 Da and the observed MW reads 1419.61 Da, that’s within acceptable range. If it reads 1405.2 Da, something is wrong — you may have a truncated or incorrect peptide.

Appearance and Physical Properties

This section describes the physical characteristics of the peptide:

  • Appearance — Usually “white to off-white lyophilized powder.” Significant discoloration (yellow, brown) can indicate degradation or contamination.
  • Solubility — Notes on how the peptide dissolves in water or other solvents.
  • pH — The pH of the reconstituted solution, if tested.

These may seem minor, but they serve as a quick sanity check. If your COA says “white powder” but you received a yellowish clump, the product may have been improperly stored or is a different batch than tested.

Amino Acid Analysis (AAA)

Not all COAs include amino acid analysis, but it’s a valuable additional test. AAA breaks the peptide down into its individual amino acids and measures their ratios. This confirms that the correct amino acids are present in the correct proportions.

What to look for: The measured amino acid ratios should closely match the theoretical ratios derived from the known sequence. Significant deviations suggest synthesis errors.

Endotoxin and Sterility Testing

Some higher-quality COAs include:

  • Endotoxin levels (measured in EU/mg via LAL test) — Important for cell culture research, as endotoxins can activate immune pathways and confound results.
  • Bioburden/sterility testing — Confirms the absence of microbial contamination.

For in-vitro research involving cell cultures, endotoxin testing is particularly important. Levels should typically be < 5 EU/mg for most research applications.

Water Content (Karl Fischer)

Some COAs report the moisture content of the lyophilized peptide, usually measured by Karl Fischer titration. Peptides are hygroscopic, and excess water content can accelerate degradation.

Acceptable water content is typically < 8% for lyophilized peptides. Higher moisture content may indicate improper lyophilization or storage.

How to Spot Red Flags

Not all COAs are created equal. Here are warning signs that should raise concerns:

1. No Chromatogram Included

A COA that states “98% purity” without including the actual HPLC chromatogram is essentially asking you to take their word for it. Reputable laboratories always include the raw data.

2. Mismatched Molecular Weight

If the observed mass spectrometry value doesn’t match the theoretical molecular weight within acceptable tolerances, the product may not be what it claims to be.

3. Generic or Template COAs

Watch out for COAs that look like they were filled in from a template with no batch-specific data. Every COA should have a unique lot number, specific test dates, and batch-specific results.

4. No Lot Number or Date

A COA without a lot number is essentially meaningless — there’s no way to trace it back to a specific production batch. Similarly, testing dates should be recent relative to when you purchased the product.

5. In-House Testing Only

While in-house testing is standard, the most trustworthy peptide suppliers also provide third-party testing from independent laboratories. This eliminates the conflict of interest inherent in a company testing its own products.

6. Suspiciously Perfect Numbers

If every metric on the COA reads as the absolute ideal value (exactly 99.0% purity, exact MW match to multiple decimal places), this may indicate fabricated results rather than actual testing.

The Importance of Third-Party Testing

Third-party testing is the gold standard for peptide quality verification. An independent laboratory has no financial incentive to inflate purity numbers or overlook issues.

Janoshik Analytical has emerged as the gold standard for independent peptide and compound testing in the research community. Their laboratory provides:

  • Independent HPLC purity analysis
  • Mass spectrometry confirmation
  • Quantitative content analysis
  • Results published with batch-specific identifiers

When evaluating a peptide supplier, check whether they submit their products for independent third-party testing. Suppliers who proactively publish third-party COAs demonstrate a level of transparency that benefits the entire research community.

Notably, Chameleon Peptides publishes COAs for all their products, including third-party test results, making it straightforward for researchers to verify the quality of what they’re purchasing before incorporating it into their research protocols.

Practical Tips for Researchers

Always Request the COA Before Purchasing

If a vendor’s website doesn’t display COAs, email them and ask. Their willingness (or reluctance) to provide documentation tells you a lot.

Match the Lot Number

When you receive your peptide, verify that the lot number on the vial matches the lot number on the COA. A mismatched lot number means the COA may not apply to your specific product.

Keep COAs on File

Maintain a record of COAs for all peptides used in your research protocols. This documentation is essential for reproducibility and auditing.

Use the Right Reconstitution Protocol

Once you’ve verified your peptide’s quality via the COA, proper reconstitution is the next critical step. Use our free reconstitution calculator to calculate your exact measurements based on the peptide amount listed on your COA.

Compare Across Batches

If you’re running long-term research protocols, compare COAs across different batches from the same supplier. Consistent results batch-to-batch indicate reliable manufacturing processes.

Understanding Peptide Content vs. Gross Weight

One commonly misunderstood aspect: the weight listed on your peptide vial is the gross weight, which includes the peptide itself plus counterions (usually acetate or TFA salts) and residual moisture.

The net peptide content — the actual amount of active peptide — is typically 60–80% of the gross weight. Some COAs list this as “peptide content” or “net peptide.” This matters when calculating concentrations for your research protocol.

For example, if your vial says “5 mg” but the COA shows 75% peptide content, the actual peptide amount is 3.75 mg. Factor this into your reconstitution calculations for maximum accuracy. Our peptide reconstitution calculator can help you determine the correct volumes.

Conclusion

Reading a peptide COA is not difficult once you understand what each section means and what to look for. The key takeaways for any researcher:

  1. HPLC purity ≥ 98% is the target for serious in-vitro research
  2. Mass spec confirmation verifies you have the correct peptide
  3. Third-party testing (especially from laboratories like Janoshik) provides the highest confidence
  4. Red flags include missing chromatograms, no lot numbers, and template-style documents
  5. Always match the lot number on your vial to the COA

Taking the time to properly evaluate your peptide COAs leads to more reliable, reproducible research outcomes. Never skip this step.

Related guides: Once you’ve verified your peptide’s quality, the next steps are reconstituting it properly and calculating your dose accurately. And make sure you’re using the right solvent — see our bacteriostatic water vs sterile water comparison.

This article is for educational and research purposes only. It does not constitute medical advice. Products referenced are for in-vitro laboratory research only.