Peptide testing methods such as high-performance liquid chromatography (HPLC), liquid chromatography–mass spectrometry (LC–MS), and nuclear magnetic resonance (NMR) spectroscopy are essential analytical tools for characterizing research-grade peptides. Each technique provides different information: HPLC assesses purity and impurity profile, LC–MS confirms molecular weight and sequence, and NMR reveals structural details. This article reviews how HPLC, LC–MS,…