Understanding Peptide Purity: HPLC vs Mass Spec — A Comprehensive Guide for Researchers When sourcing research peptides, purity is the single most critical quality parameter. An impure compound doesn't just waste money — it contaminates experimental data, produces misleading results, and can fundamentally compromise the validity of your research. Yet the way purity is measured, reported, and verified varies considerably across the peptide supply industry, and not all certificates of analysis are created equal. This guide explains the two dominant analytical techniques used to assess peptide purity — High-Performance Liquid Chromatography (HPLC) and Mass Spectrometry (MS) — how each method works, what each actually measures, and how to interpret the combined results when evaluating a supplier's analytical documentation. ## What Is Peptide Purity? Peptide purity refers to the proportion of a sample that consists of the intended target peptide, expressed as a percentage. A purity of ≥