Commissioning a peptide synthesis service on purity and analysis rather than on price per residue: what length, sequence difficulty and modification do to a quotation, when a peptide synthesis machine in house beats buying and when it does not, where peptide nucleic acid synthesis is a different chemistry entirely, what a myostatin inhibitor peptide, a cgrp peptide, dermorphin bought as a dermorphin peptide, a lipopeptide and other named sequences each need proving before use, what peptide testing, peptide analysis and peptide mapping services should report and what a testing tube of material has to arrive with, and why the certificate rather than the tube is what you are actually buying

Placing the order

1. Set the purity grade against the use. Crude material is adequate for screening a library of sequences. Purified material is required for quantitative assays, and high purity with full characterisation for anything going into animals. Ordering higher than needed wastes money; ordering lower produces results attributable to the impurities.
2. Ask what the stated mass actually contains. A quoted quantity is often gross weight including counterion and water, which can be a substantial fraction. Ask for net peptide content, and if the assay depends on concentration, ask for amino acid analysis rather than a nominal figure.
3. Declare modifications and the counterion. Terminal capping, labels, cyclisation, phosphorylation and unusual residues each change the synthesis and the price. The counterion matters too: a residue from purification can be biologically active in cell assays, so specify it where it could interfere.
4. Flag difficult sequences early. Long sequences, hydrophobic stretches, multiple cysteines and aggregation prone regions are what make a synthesis fail or a purification lose most of the material. Suppliers will tell you before quoting if asked, and a redesign at that stage is cheap.
5. Specify the analytical package. Mass confirmation and a purity chromatogram as a minimum, with amino acid analysis where quantity matters and a disulphide assignment where folding matters. The chromatogram should come with the material, not on request.
6. Plan storage and handling on arrival. Peptides are hygroscopic and many oxidise. Aliquot from a single dissolution rather than repeatedly opening a cold vial into a humid room, and record the solvent and concentration used.

What you are buying is the certificate

Two suppliers can deliver the same sequence at the same nominal purity and the same price, and one lot will behave in the assay while the other will not. The difference is in what was measured and reported: net peptide content, the identity of the impurities, the counterion, the water.

Compare suppliers on the analytical package before comparing them on price. It is the only part of the transaction that tells you what is in the tube.

Named sequences still need proving

Ordering a well known sequence does not remove the obligation to confirm identity and behaviour in your own hands. Sequence errors, incorrect modification positions and mislabelled tubes all happen, and a biological effect built on the wrong molecule is a long detour.

Confirm mass on arrival where you can, run a positive control in the first experiment, and keep the certificate with the lot so a later question has an answer.

Common questions

Why is my peptide less soluble than expected?

Composition, usually. Hydrophobic and aggregation prone sequences need a solvent strategy rather than water, and the order in which solvents are added matters. Ask the supplier for a recommended dissolution before assuming the material is faulty.

What does purity on a certificate mean?

The area of the main peak in a stated chromatographic method, which says nothing about what the other peaks are or about water and counterion content. Two certificates quoting the same purity can describe materially different tubes.

Is in house synthesis worth it?

For groups making many sequences continuously, yes, because turnaround becomes hours rather than weeks. For occasional peptides it rarely is once instrument, reagents, purification and the trained person are counted.

When is amino acid analysis needed?

Whenever the result depends on knowing the concentration accurately, for example potency work or binding constants. Weighing a hygroscopic powder of unknown net content is not a quantitative operation.

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