How to Read a Certificate of Analysis (COA) for Research Peptides

What Is a Certificate of Analysis?

A Certificate of Analysis (COA) is a document issued by a testing laboratory that confirms the identity, purity, and quality of a research compound. For peptide researchers, the COA is one of the most important documents you will encounter — it provides the objective, third-party verification that your compounds meet the standards required for reliable research.

At Pept, every product ships with a COA. We believe transparency is non-negotiable when it comes to research-grade compounds. This guide will walk you through how to read and interpret a peptide COA so you can evaluate compound quality with confidence.

Why COAs Matter in Peptide Research

The quality of research compounds directly affects the reliability and reproducibility of experimental results. Without a COA, there is no way to verify that a peptide meets the purity and identity standards necessary for valid research. A COA serves as proof that the compound has been independently tested and meets stated specifications. It also provides a reference document for documenting compound quality in research records and publications, and helps researchers identify potential issues before they affect experimental outcomes.

Key Components of a Peptide COA

A comprehensive COA for research peptides should include several critical sections. The first is compound identification, which lists the peptide name, catalogue or batch number, molecular formula, and molecular weight. This section confirms you have the correct compound. The second is the purity analysis, typically performed using High-Performance Liquid Chromatography (HPLC). This is often the most important number on the COA — research-grade peptides should typically show purity of 95% or higher, with premium compounds reaching 98% or above.

The third key component is mass spectrometry (MS) results, which confirm that the peptide has the correct molecular weight. This verifies the compound's identity at the molecular level. The expected molecular weight should match the theoretical weight for the peptide sequence. The fourth is amino acid analysis, which verifies the composition of the peptide by measuring the ratio of each amino acid present. This confirms the peptide was synthesised with the correct sequence.

Understanding HPLC Purity Results

HPLC is the gold standard for peptide purity analysis. The technique separates compounds in a mixture and measures their relative abundance. On a COA, you will typically see the HPLC purity expressed as a percentage, such as 98.5%. This means that 98.5% of the sample consists of the target peptide, with the remaining 1.5% being impurities such as deletion sequences, truncated peptides, or other synthesis byproducts. For most research applications, a purity of 95% or higher is considered acceptable, while purities above 98% are ideal for sensitive assays.

Reading Mass Spectrometry Data

Mass spectrometry confirms the identity of a peptide by measuring its molecular weight. The COA will show the observed mass alongside the expected (theoretical) mass. These values should be very close — typically within 1 dalton of each other. A significant discrepancy between observed and expected mass could indicate the wrong compound, an incomplete synthesis, or post-translational modifications.

Endotoxin Testing

Some COAs include endotoxin testing results, particularly for compounds intended for use in cell culture or in vivo research models. Endotoxins are bacterial contaminants that can interfere with biological experiments. The test is typically performed using the Limulus Amebocyte Lysate (LAL) assay, and results are reported in Endotoxin Units per milligram (EU/mg). Low endotoxin levels are critical for research involving live cells or animal models.

Red Flags to Watch For

When reviewing a COA, there are several warning signs that should prompt further investigation. These include missing or incomplete data where key sections like HPLC purity or MS results are absent, unusually round numbers that may indicate fabricated results rather than actual measurements, no batch number making it impossible to trace the specific production lot, the COA not matching the product where the compound name or specifications differ from what was ordered, and no laboratory identification meaning there is no indication of which lab performed the testing.

Pept's Commitment to Transparency

At Pept, we publish COAs for all our products and include one with every order. Our compounds undergo rigorous third-party testing by independent laboratories. We believe that access to comprehensive testing documentation should be standard practice, not a premium add-on. If you ever have questions about a COA or need additional testing documentation, our team is here to help.

All Pept products are for research use only.