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Peptide sequence or name

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Synthesis and instrument

Coupling reagent Mass spectrometer

Piperidine for Fmoc removal Ac₂O capping after each coupling

Thiol scavenger in cleavage (EDT, DTT) Include Na⁺ and K⁺ adducts

Scan range m/z

How to write a sequence

Known peptides by name (insulin, oxytocin, glucagon, exenatide, amyloid beta 1-42 …). Several chains: join them with + and add the bridges, e.g. GIVEQCCTSICSLYQLENYCN + FVNQHLCGSHLVEALYLVCGERGFFYTPKT, 3 disulfides. A single chain with a bridge: CYIQNCPLG-NH2, 1 disulfide.

Reactive handles go on like caps: BCN-, DBCO-, ClAc- (chloroacetyl), Mal- (maleimide), Pentynoyl-, or on a Lys side chain as K(BCN). Conjugates: scaffold with 2x partner via SPAAC; chemistry can be SPAAC, CuAAC, S-alkylation, maleimide or disulfide, e.g. Ac-K(N3)GK(N3)-NH2 with 2x BCN-GGRGDS-OH via SPAAC. One-letter Ac-K(N3)GDF-NH2, three-letter Ac-Lys(N3)-Gly-dSer-NH2 (hyphens, spaces or none), BILN, linear HELM, or reagent names like [Fmoc-Lys(Mtt)-OH]. Lowercase one-letter means D. Non-natural residues go in brackets: [Aib], [O2Oc]. A residue Chemtize does not know can be looked up by name.

What is in my sample?

Type the m/z values your spectrum shows

or drop an LC-MS file here
mzML run, or a spectrum exported as CSV

Each value is matched against your product, its impurities, adducts and isotope peaks. A value nothing explains is marked as unexplained. Nothing is guessed.

Reference

Masses to look for

What a synthesis of this sequence typically gives, most likely first.

What	Likelihood	Look for m/z	Δ mass (Da)

Dissolving and storing

Make a solutionpowder → volume

Powder (mg) Purity (%) Peptide content (%) Concentration Unit

Peptide content is the share of the powder that is peptide, not counter-ions or water. Take it from the certificate, or from salt forms below.

Concentration from UV (A280)

Measured A280 Path length (cm) Cysteines

Charge and isoelectric point

Salt forms and peptide content

Hydrophobicity

Isotope pattern

Charge state

Sequence and composition

Add a building block

Type the reagent name as it is on the bottle, or paste a SMILES. Only the name is sent to PubChem, never a sequence.

Library

Residues

Write	Name	Residue formula	Mono (Da)	Notes

Groups

Write	Name	Adds	Mono (Da)

Impurity rules

Edit them in data/rules.yaml. The page picks up changes on the next calculation.

Species	Δ (Da)	Likelihood	Why