How it works
The first residue is attached to a resin bead, and the chain is extended by repeating a cycle: deprotect the reactive end, couple the next protected amino acid, wash away the excess, and repeat. Because the peptide is held on the solid support, purification between steps is just rinsing.
Chains are typically assembled from the C-terminus toward the N-terminus — the opposite direction to how a sequence is read — with side-chain protecting groups keeping each coupling specific. When the sequence is complete, the peptide is cleaved from the resin and deprotected.
SPPS is a construction method, not a characterization method. It is how a peptide is made; whether the intended sequence was actually obtained is a separate question, answered afterward by mass spectrometry and HPLC.
Why it matters
SPPS is why research peptides can carry the modifications they do. Non-standard residues, terminal acetylation or amidation, and other alterations are introduced as the chain is built, which is why the compound pages can list such specific compositional detail.
Its stepwise nature is also where characteristic impurities come from: an incomplete coupling or a deletion leaves a closely related sequence behind, exactly the kind of impurity that RP-HPLC is used to resolve and quantify.
Because synthesis and verification are separate, a well-made peptide still requires proof: identity by ESI-MS against the computed mass, purity by RP-HPLC against the chromatogram.
At Lineará
The modifications SPPS makes possible — non-standard residues, terminal chemistry, bridges — are exactly the compositional details drawn on the compound pages and reconciled in the identifier work.
The synthesis-related impurities SPPS can leave behind are the reason purity is measured by RP-HPLC and reported per lot on every certificate.