How to (and How Not to) Read a Certificate of Analysis (COA

In the research peptide industry, few documents are referenced more often—and understood less—than the Certificate of Analysis, commonly known as a COA.

Many researchers have learned to look for a purity percentage and stop there. If the report says “99% purity,” the assumption is often that the product is high quality.

Unfortunately, that’s not how analytical testing works.

A COA can provide valuable information about a material, but only if you know what you’re looking at. More importantly, understanding what a COA does not tell you is just as critical as understanding what it does.

What Is a COA?

A Certificate of Analysis is a document that summarizes the results of laboratory testing performed on a specific batch of material.

Depending on the testing performed, a COA may provide information about:

• Identity
• Purity
• Quantitation
• Sterility
• Endotoxin levels
• Heavy metals
• Appearance
• Batch information

Not all COAs are created equal. Some provide meaningful analytical data, while others contain little more than a purity percentage and a logo.

The Most Common Mistake: Looking Only at Purity

The first thing many researchers search for is a purity value.

For example:

Purity: 99.2%

While purity is important, it is only one piece of the puzzle.

Purity testing attempts to determine how much of the sample consists of the target compound versus impurities. What it does not tell you is whether the compound is actually what the label claims it is.

A sample can be highly pure and still fail identity testing.

How Not to Read a COA

❌ “It says 99% purity, so it must be good.”

This is one of the most common misconceptions in the industry.

How to Read a COA

✅ Ask what testing was performed beyond purity.

Identity testing, sterility screening, endotoxin testing, and heavy metal analysis all provide important information that purity alone cannot.

Identity Testing: The First Thing You Should Look For

Before asking how pure something is, researchers should first ask:

Is it actually what the label says it is?

Identity testing is designed to verify the molecular identity of a material.

Without identity testing, a purity result has limited value because purity does not confirm the actual substance being tested.

A complete testing program should begin with confirming identity before evaluating other quality attributes.

Understanding HPLC Results

High Performance Liquid Chromatography (HPLC) is one of the most common analytical techniques used in peptide testing.

An HPLC chromatogram displays peaks representing compounds detected within the sample.

Researchers often focus exclusively on the largest peak, but it’s important to understand that:

• The largest peak is assumed to represent the target compound.
• Smaller peaks may represent impurities.
• Peak area is used to estimate purity.

While HPLC can be extremely useful, the results are only as meaningful as the testing methods and interpretation behind them.

What a COA Usually Doesn’t Tell You

Many COAs stop at identity and purity.

That means they may provide no information regarding:

• Sterility
• Endotoxins
• Heavy metals
• Residual contaminants

These factors cannot be determined simply by looking at an HPLC report.

Sterility Matters

A material can pass identity testing.

A material can pass purity testing.

A material can still fail sterility testing.

Sterility testing evaluates whether viable microorganisms are present in a sample. This is a completely separate measurement from purity and identity.

When researchers focus exclusively on purity percentages, sterility is often overlooked entirely.

Endotoxins Matter Too

Another common misconception is that sterile automatically means safe.

It does not.

Even when viable microorganisms are absent, endotoxins can remain.

Endotoxins are bacterial byproducts that require specialized testing methods, such as USP <85> bacterial endotoxin testing, to detect.

This is why sterility testing and endotoxin testing should be viewed as complementary—not interchangeable.

Heavy Metals: The Overlooked Category

Heavy metal analysis is often one of the least discussed aspects of quality testing.

Using techniques such as ICP-MS, laboratories can screen for elements such as:

• Lead
• Arsenic
• Cadmium
• Mercury

While many researchers never think to ask about heavy metal testing, it remains an important component of a comprehensive quality program.

Red Flags to Watch For

Not all COAs deserve the same level of trust.

Some warning signs include:

Broken QR Codes

A QR code that doesn’t resolve to a laboratory report should raise questions.

Missing Batch Numbers

Every COA should clearly identify the batch being tested.

Generic Reports

A COA that appears identical across multiple batches may indicate that testing is not being performed consistently.

Missing Laboratory Information

Researchers should be able to determine who performed the testing.

Cropped or Incomplete Reports

Missing pages, incomplete chromatograms, or partial screenshots should always be treated cautiously.

“COA Available Upon Request”

Transparency delayed is often transparency denied.

A Better Way to Evaluate Quality

Instead of asking:

“What’s the purity?”

Consider asking:

• Was identity confirmed?
• Was purity tested?
• Was quantitation performed?
• Was sterility evaluated?
• Were endotoxins screened?
• Were heavy metals analyzed?

The answers to those questions provide a far more complete picture of quality than a single purity percentage ever could.

The Bottom Line

A COA is only as valuable as the testing behind it.

Researchers who focus exclusively on purity percentages often miss some of the most important quality indicators available. Identity, sterility, endotoxin screening, heavy metal analysis, and quantitation all contribute to a more complete understanding of a material.

The next time you review a COA, don’t just look for the biggest number on the page.

Look for the tests that prove what’s actually in the vial.