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When comparing research peptides, you will often see figures like “95% purity”, references to “HPLC”, and mention of a “COA”. These terms directly affect the quality and reproducibility of research work — so it is worth understanding exactly what they mean.
What does “purity” actually measure?
Purity refers to the proportion of the sample that is the target peptide, versus everything else — incomplete sequences, by-products of synthesis, salts and residual solvents. A “95%” figure means the target peptide accounts for 95% of the measured peptide content, with the remainder being related impurities.
How is purity tested? (HPLC)
HPLC stands for High-Performance Liquid Chromatography. It separates the components of a sample as they pass through a column at different rates, producing a chromatogram — a graph of peaks. The main peak represents the target peptide; smaller peaks represent impurities. The relative size of the main peak gives the purity percentage.
What is a COA?
A Certificate of Analysis (COA) is the document that reports these results. A typical COA includes:
- The peptide name and sequence
- The purity percentage from HPLC
- Mass spectrometry (MS) confirmation of molecular weight
- Batch/lot identification
Together, HPLC confirms how pure the peptide is, and MS confirms it is the correct peptide.
Why purity matters for research
Higher purity means fewer confounding variables. Impurities can interfere with results and reduce reproducibility between batches. This is why documented purity grades — such as our 95% and premium listings — are an important part of transparent sourcing.
Reading a purity claim critically
A responsible purity claim is backed by testing, not just stated. When comparing suppliers, look for whether the figure is supported by HPLC and MS data rather than an unverified number.
Summary
Purity percentage, HPLC and the COA are three parts of the same quality story: the percentage tells you how clean the peptide is, HPLC is how it is measured, and the COA is the paperwork that proves it. Understanding these terms helps you make informed, like-for-like comparisons.
All items are sold for research purposes only.