Crude peptide and purification

What crude material contains

The target sequence, deletion sequences missing one or more residues, truncated chains, incompletely deprotected species, and residual reagents and solvents. Depending on the sequence, the target may be well under half the mass.

Preparative chromatography

Purification usually uses reversed-phase chromatography at scale: the mixture is loaded onto a column and a solvent gradient elutes components at different times. Fractions are collected and analysed, and only those meeting specification are pooled.

The trade-off is yield against purity. Collecting narrowly around the target peak gives a purer product and less of it; collecting widely gives more material and more closely related impurities.

Why closely related impurities are the hard part

A deletion sequence differing by a single residue behaves almost identically on a column. Separating it requires a shallow gradient and patience. This is the step where cost and quality genuinely trade against each other, and where the difference between suppliers usually lies.

After purification

Pooled fractions are freeze-dried to remove solvent and water. The dried solid is the material that goes into vials, and it is analysed again before release.