How to Verify Peptide Quality: COA Guide and Red Flags

The research peptide market has a quality problem. Independent testing has shown that some vendors sell peptides with purities far below what is advertised, while others sell mislabeled or contaminated products entirely. A 2019 analysis published in Drug Testing and Analysis found that nearly 40% of peptides purchased from online sources did not match label claims (PMID: 30950187).

Your best defense is knowing how to read a Certificate of Analysis (COA) and spot fakes. This guide breaks down exactly what to look for – and what should send you running.

What Is a Certificate of Analysis (COA)?

A Certificate of Analysis is a document provided by a peptide manufacturer or supplier that reports the results of quality testing on a specific batch of product. A legitimate COA should include:

• Product name and catalog number
• Batch or lot number – unique to that production run
• Date of analysis
• Testing methods used (HPLC, Mass Spectrometry, etc.)
• Results – purity percentage, molecular weight confirmation
• Appearance and physical description
• Lab name or analyst identification

A COA is only as trustworthy as the lab that produced it. In-house COAs (generated by the vendor’s own lab) carry less weight than third-party COAs from independent testing facilities. The best suppliers provide both.

How to Read HPLC Results

High-Performance Liquid Chromatography (HPLC) is the gold standard for peptide purity testing. It separates the components of a sample and shows what percentage of the total material is the target peptide versus impurities.

Key Things to Look For

Purity percentage: This is the headline number. Research-grade peptides should show 98% or higher purity. Anything below 95% is a red flag for research applications. The purity is calculated from the area under the main peak divided by the total area of all peaks in the chromatogram.

The chromatogram itself: A good COA includes the actual HPLC chromatogram – the graph showing peaks. You should see one dominant peak (your peptide) with minimal smaller peaks (impurities). If a COA reports 99% purity but does not include the chromatogram, that is a warning sign.

Retention time: This is when the peptide elutes (comes off) the column, measured in minutes. Each peptide has a characteristic retention time under standard conditions. While you may not know the expected time, it should be consistent across batches from the same lab.

Method details: A legitimate HPLC report lists the column type, mobile phase composition, flow rate, and detection wavelength (typically 220 nm for peptides). If these details are missing, the report is incomplete.

Common Impurities

Minor peaks on the chromatogram typically represent:

• Deletion sequences – peptide chains missing one or more amino acids
• Truncated sequences – incomplete synthesis products
• Oxidized forms – methionine or tryptophan residues that have been oxidized
• Residual solvents – TFA (trifluoroacetic acid) or acetonitrile from the purification process

Understanding Mass Spectrometry Data

While HPLC tells you how pure the peptide is, Mass Spectrometry (MS) tells you what the peptide is. MS measures the molecular weight of the compound and confirms its identity.

What to Check

Observed molecular weight vs. expected molecular weight: These should match within 1 Dalton (Da) for most peptides. For example, BPC-157 has an expected molecular weight of approximately 1419.5 Da. If the MS data shows 1419.4 Da, that is a match. If it shows 1350 Da or 1500 Da, the product is not BPC-157.

MS spectrum: Like the HPLC chromatogram, the actual spectrum should be included. You will typically see the [M+H]+ peak (molecular weight plus one hydrogen) as the dominant signal, along with multiply charged ions like [M+2H]2+ at roughly half the molecular weight.

Method type: ESI-MS (Electrospray Ionization Mass Spectrometry) and MALDI-TOF are the two most common methods for peptide analysis. Either is acceptable. The method should be stated on the COA.

Why MS Matters

HPLC alone cannot confirm identity – it only measures purity. A vial could contain a 99% pure peptide that is the wrong peptide entirely. MS data closes this gap. Any supplier that provides HPLC but not MS data is giving you an incomplete picture.

Red Flags in Fake or Unreliable COAs

As peptide demand has grown, so have the number of suppliers producing fake or misleading COAs. Here is what to watch for:

1. No Batch Number

A COA without a batch or lot number is useless. It cannot be traced to any specific production run, which means the supplier may be using a single generic COA for all their products.

2. Suspiciously Round Numbers

Real lab results almost never come out to exactly 99.00% or 98.00%. Legitimate results look like 98.73% or 99.14%. Perfectly round purity numbers suggest the document was fabricated rather than generated from actual testing.

3. Missing Chromatograms or Spectra

A COA that reports purity or molecular weight numbers without including the actual graphs is incomplete at best and fabricated at worst. The raw data – the chromatogram from HPLC and the spectrum from MS – should always be present.

4. No Lab Identification

Who performed the testing? A real COA identifies the lab, the analyst, and often includes a signature or stamp. If there is no lab name or the document looks like it was made in Microsoft Word with no institutional branding, be skeptical.

5. Generic Templates Used Across Products

If every COA from a supplier uses the exact same template with only the peptide name and purity number changed – same retention times, same peak shapes, same everything – those documents are likely fabricated. Real chromatograms look different for different peptides.

6. Refusal to Provide Batch-Specific COAs

If you request a COA for your specific batch and the supplier cannot or will not provide one, that is a major red flag. Legitimate manufacturers test every batch and can provide documentation for any lot number.

7. COA Date Predates Your Batch

If the COA is dated 2023 but you ordered in 2026, the document likely does not correspond to your product. Fresh batches should have recent testing dates.

Trusted Third-Party Testing Labs

For researchers who want independent verification beyond the supplier’s COA, several labs offer peptide testing services:

• Janoshik Analytical – Popular in the research community, offers HPLC and MS testing for peptides at reasonable prices (typically $80-120 per sample)
• Colmaric Analyticals – Australian lab offering peptide purity and identity testing
• Veritest Labs – US-based analytical testing for research compounds
• ChemAnalytical – Provides HPLC, MS, and endotoxin testing for peptides

Third-party testing typically costs $50-150 per sample, depending on the tests requested. For expensive peptides or large orders, this cost is a worthwhile investment in quality assurance.

How to Request Batch-Specific Testing

Before purchasing, take these steps to verify quality:

Step 1: Ask for the COA Before Buying

Email the supplier and request a COA for the current batch of the peptide you want to purchase. A good supplier will send this within 24 hours. If they do not have one available or redirect you to a generic document, consider a different supplier.

Step 2: Cross-Check the Batch Number

When your order arrives, verify that the batch number on the vial label matches the batch number on the COA you were provided. Mismatches indicate the COA may not apply to your product.

Step 3: Submit for Independent Testing

For high-value research, send a sample to one of the third-party labs listed above. You will typically need to mail a small amount of the lyophilized peptide (1-2 mg is usually sufficient). Results come back within 1-3 weeks depending on the lab.

Step 4: Compare Results

Compare the third-party results to the supplier’s COA. The purity percentage should be within 1-2% of each other. The molecular weight should match exactly. Significant discrepancies indicate a problem with the supplier’s claims.

Choosing a Trustworthy Supplier

The easiest way to avoid quality issues is to buy from suppliers with established reputations for transparency and testing. Look for vendors that:

• Provide batch-specific COAs automatically with every order
• Include both HPLC and MS data on their COAs
• Use third-party testing in addition to in-house testing
• Have consistently positive reviews from the research community
• Offer refunds or replacements for quality issues

We have reviewed and compared the top suppliers on our best peptide companies page, with special attention to their quality verification practices and testing transparency.

For a practical guide on handling peptides once you have verified their quality, check out our step-by-step reconstitution guide.