Understanding Peptide Purity and Certificates of Analysis

Purity is the single most important quality metric for a research peptide, because impurities — truncated sequences, deletion products, or residual synthesis reagents — can confound experimental results. Understanding how purity is measured and documented helps researchers compare suppliers on something more meaningful than price.

How purity is measured: HPLC

High-performance liquid chromatography (HPLC) separates the components of a sample as they pass through a column. The target peptide appears as a peak, and impurities appear as additional peaks. Purity is reported as the area of the main peak as a percentage of all peaks. A “≥99%” specification means the target peptide accounts for at least 99% of the detected material by this method.

How identity is confirmed: mass spectrometry

HPLC tells you how much of the sample is one dominant species, but not what that species is. Mass spectrometry (MS) measures the molecular weight of the peptide and confirms it matches the expected sequence. A COA that reports both HPLC purity and an MS-confirmed mass gives confidence in both purity and identity.

Reading a certificate of analysis

• Product name and batch / lot number — ties the document to a specific production run
• HPLC purity (%) — the headline purity figure
• Mass spectrometry result — confirms the molecular weight / identity
• Endotoxin level — relevant for sensitive cell-culture work
• Appearance and net peptide content — physical description and quantity

Why “third-party tested” matters

An in-house COA is produced by the manufacturer; a third-party COA is produced by an independent laboratory. Independent verification reduces the risk of conflicts of interest and is a stronger signal of quality. When a supplier publishes batch-specific COAs that a buyer can match to the lot they received, the documentation is verifiable rather than decorative.