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Glossary

Terms beginning with D

12 of 238 glossary terms.

Drift: Slow monotonic change in the baseline across a run. Caused by mobile-phase absorbance changing with organic fraction, or by column temperature not being controlled.
Drop-line integration: Separating two overlapping peaks with a vertical line dropped from the valley between them. Unbiased when the peaks are of comparable size.
Deconvolution: Recovering a neutral mass from a set of observed m/z values across charge states. Self-checking: two charge states give two independent estimates.
Deamidation: Conversion of asparagine to aspartate or glutamine to glutamate, +0.984 Da. A storage degradation route, accelerated above pH 7.
Deletion sequence: A peptide missing one or more residues from an incomplete coupling. Mass difference equals the missing residue mass. A synthesis finding: it does not form in a vial.
Diastereomer: A stereoisomer arising from inversion at one chiral centre. Same formula, same mass, same UV spectrum, often much less active. The impurity no mass spectrum finds.
Diketopiperazine: A cyclic dipeptide, −18.011 Da, formed by intramolecular attack at the N-terminus. Common in proline-rich short peptides.
Dimer: Two molecules covalently linked, usually through a disulfide. Mass is roughly double the parent, minus 2.016 Da for a disulfide linkage.
Disulfide scrambling: Cysteines paired in an incorrect combination. Mass-identical to correct pairing and only detectable by peptide mapping or comparison against a folded reference.
Digit preference: Non-uniform distribution of terminal digits in reported figures. A real integrated area does not land on a round number repeatedly.
Documentation-completeness score: The index's 0–100 rubric for what a supplier's certificates actually state. Rubric published in full at /suppliers/methodology/.
Desiccant: A moisture-absorbing material included in packaging. Its presence or absence changes the water content measured on arrival for hygroscopic material.