What Is a Certificate of Analysis?

A Certificate of Analysis (COA) is an analytical document issued by the manufacturer or an independent testing laboratory that reports the results of quality testing performed on a specific production lot of a compound. It serves as the primary quality assurance document for research reagents and is the closest thing to a “receipt of quality” that exists in the supply chain.

A COA is not a marketing document. It is not a certificate of “goodness” or a general quality claim. It documents specific, measurable test results for a specific batch. Understanding this distinction is the first step in reading one correctly.

Key Sections of a COA

Compound Identification

This section should include the compound name, CAS number, molecular formula, molecular weight, and lot/batch number. The lot number is critical — it ties the test results to the specific batch you received. If the lot number on your vial does not match the lot number on the COA, the document does not apply to your product.

Purity (HPLC)

The most important result on most peptide COAs is the HPLC purity value. This represents the percentage of the total material that is the target compound, as measured by high-performance liquid chromatography. A result of ≥98% means that at least 98% of the detected material is the compound of interest, with ≤2% being other species (synthesis impurities, degradation products, or related substances).

Look for the testing method description: reverse-phase HPLC is standard for peptides. The COA should specify the column type, mobile phase, and detection wavelength — though not all manufacturers include this level of detail.

Identity Confirmation

A purity number alone does not confirm identity — it only tells you that the material is pure, not that it is what it claims to be. Identity confirmation typically comes from mass spectrometry (MS), which verifies the molecular weight matches the expected value. Look for an MS result showing the observed mass matches the theoretical mass within acceptable tolerance.

Appearance and Physical Properties

The COA may describe the physical appearance (e.g., “white to off-white lyophilized powder”), solubility, and pH. These are less quantitative than HPLC and MS but provide baseline expectations for what you should see when you open the vial.

Red Flags on a COA

Missing lot number or batch number (makes the document unverifiable). No HPLC result or a purity result stated as a range without a specific measured value. No mass spectrometry confirmation of identity. Generic or template-style COAs that do not appear to reflect actual testing. COAs dated significantly before or after the labeled production date. Results that exactly match the specification with no variance (e.g., “Purity: 99.0%” every time — real analytical testing produces variable results).

What a Good COA Looks Like

A trustworthy COA includes a specific lot number matching your product, a measured HPLC purity value (not a range), mass spectrometry confirmation, a specific test date, identification of the testing laboratory or manufacturer, and method details or references. Every compound from Vial & Error Labs ships with a lot-specific COA from the manufacturer. Our COA Library provides digital access to these documents by SKU or lot number. If you have questions about a specific COA, contact us. For research use only.