Skip to content

Glossary

Terms beginning with C

23 of 238 glossary terms.

Capacity factor (k'): Retention relative to the unretained time: (t − t₀)/t₀. A k' below 1 means the compound is barely retained and is not usefully separated.
Column dead time (t₀): The time taken for an unretained species to traverse the column. Everything eluting at t₀ is unseparated.
Core–shell particle: A stationary-phase particle with a solid core and a porous shell. Shorter diffusion path, sharper peaks, lower backpressure than a fully porous particle of the same size.
C18: Octadecyl-bonded silica: the standard reverse-phase stationary phase for peptides. Retention scales with the analyte's exposed hydrophobic surface, not with its mass.
Chromophore: The part of a molecule responsible for UV absorbance. In peptides: the amide bond below 230 nm, and Trp/Tyr near 280 nm.
Carry-over: Sample residue transferred from one injection to the next, usually in the autosampler needle or loop. Quantified by a blank after a high-concentration injection.
Charge state (z): The number of protons carried by an ion. Observed m/z = (M + z × 1.007276)/z. Two adjacent charge states determine z without assumption.
Charge-state envelope: The distribution of intensities across charge states. Its shape carries conformational information: compact molecules ionise at lower charge.
Counter-ion: The anion paired with a peptide's basic residues in the isolated salt. Usually trifluoroacetate or acetate. Mass in the vial that is not peptide.
Coulometric titration: A titration in which the titrant is generated electrochemically and quantified from the charge passed. For water: 10.71 coulombs per milligram.
Capping: Deliberately acetylating unreacted amines during synthesis so failed couplings terminate as short capped species rather than continuing as deletion sequences.
Coupling efficiency: The fraction of resin-bound chains that react at each synthesis step. At 99.5 % per step, a 40-mer is 82 % full-length before purification.
C-terminal amide: A peptide ending in -CONH₂ rather than -COOH. Frequently required for activity; its hydrolysis to the free acid is a +0.984 Da impurity.
Cleavage cocktail: The acidic mixture that releases the peptide from the resin and removes side-chain protection. Scavengers in it suppress alkylation artefacts.
Collapse temperature: The temperature above which a freeze-concentrated matrix loses structure during primary drying. Exceeding it gives a collapsed cake and high residual moisture.
Confidence interval: A range that would contain the true value in a stated proportion of repeated samples. Wide intervals on small cells are the honest presentation.
Certificate of analysis (COA): A document stating test results for a specific lot. In this market frequently lacking a method section, a lot number, or both.
Chain of custody: The documented sequence of possession of a sample from acquisition to analysis. Determines what a result can be attributed to.
COA divergence: The supplier's declared purity minus the median of independent measurements on the same lot. Flagged above 1.5 pp by rule AX-R05.
Cake: The porous solid remaining after lyophilisation. Its appearance is a direct readout of cycle control.
Cake shrinkage: Separation of the cake from the vial wall. Indicates moisture uptake after drying, or a closure-integrity failure.
Closure integrity: Whether the stopper and crimp maintain the container's seal and vacuum. A failure lets in moisture and oxygen.
Cold chain: Maintaining a controlled low temperature through shipping and storage. Its failure has a specific analytical signature: oxidation and, for disulfides, reduction.