Understanding Peptide Purity and the Certificate of Analysis (COA)

In peptide research, the quality of your starting material sets a ceiling on the quality of your results. Two compounds with the same name but different purity can behave very differently in an experiment. This article explains how purity is measured, what a Certificate of Analysis (COA) tells you, and why batch-level documentation matters.

What “purity” actually means

Purity refers to the proportion of the target peptide in a sample relative to impurities such as truncated sequences, deletion products, or residual synthesis reagents. It is most commonly reported as a percentage — for example, “99.1% by HPLC.” Higher purity means fewer confounding variables in your research.

How purity is verified

• HPLC (High-Performance Liquid Chromatography) separates the components of a sample so that the main peak (your target peptide) can be measured against impurity peaks. The result is the purity percentage.
• Mass Spectrometry (MS) measures the molecular weight of the peptide, confirming that the correct sequence was synthesized and that the observed mass matches the theoretical mass.

Together, HPLC and MS answer the two essential questions: Is it the right molecule? and How pure is it?

How to read a Certificate of Analysis

A COA is a batch-specific document that typically lists the product name and sequence, the batch or lot number, the HPLC purity result (often with the chromatogram), the MS result, appearance, and the test date. Because it is tied to a specific batch, a COA reflects the exact material you received — not a generic specification.

At GetAll Peptides, the compounds we carry are verified to greater than 99% purity, with batch documentation available. You can browse our research peptide catalog to see the range we supply.

Why batch-level documentation matters

Reproducibility depends on knowing precisely what you are working with. Batch-specific COAs let a laboratory trace results back to a defined input, compare lots over time, and maintain proper records. It is one of the simplest and most important markers of a serious supplier.