Solid-phase synthesis step by step, and where the impurities come from.
Solid-phase peptide synthesis builds a chain from the C-terminus while it is attached to a resin. Each amino acid is protected, coupled, washed, and deprotected in sequence. The completed chain is cleaved from the resin and then purified and characterized.
Impurities can come from incomplete coupling, deletion sequences, side reactions, protecting-group remnants, or purification limits. HPLC and mass spectrometry help describe what was measured, but each method still has a defined scope.