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Glossary

Terms beginning with P

22 of 238 glossary terms.

Peak apex: The point of maximum detector response within a peak. Where the UV spectrum and mass spectrum are usually taken.
Peak integration: Determining a peak's area by defining its start, end and baseline. The step where a purity figure is actually decided, and the one least often documented.
Peak purity: Evidence from a photodiode-array or mass detector that the spectrum is constant across a peak, indicating no co-eluting species with a different chromophore. Silent on diastereomers.
Photodiode array (PDA): A UV detector acquiring a full spectrum at every time point rather than one or two wavelengths. Enables peak-purity assessment and the 280/214 ratio.
Plate count (N): Column efficiency: N = 5.54 (t/w½)². Higher is sharper. The index requires N ≥ 20,000 for a main peak.
Plate height: Column length divided by plate count. A physical measure of the efficiency per unit length, independent of column length.
ppm: Parts per million. Used for mass accuracy: ppm = (observed − theoretical)/theoretical × 10⁶.
Peptide content: The fraction of total mass that is peptide, %w/w. Distinct from purity, which is a fraction of detected chromatographic area.
Pyroglutamate: Cyclisation of an N-terminal glutamine or glutamate, −17.027 or −18.011 Da. Also the native N-terminus of GnRH, where acid stress opens it to +18.011.
PEGylation: Covalent attachment of polyethylene glycol. The polymer is polydisperse, so a PEGylated peptide has no single mass and no meaningful single purity figure.
Polydispersity: A distribution of molecular masses rather than a single value. Characteristic of synthetic polymers and therefore of PEG conjugates.
Pseudoproline: A dipeptide building block that temporarily disrupts secondary structure on-resin, used to get through aggregation-prone sequences.
Preparative HPLC: Chromatography at scale to purify the crude peptide. The fraction cut sets the purity/yield trade, and a wide cut is visible in the impurity profile.
Percentage point (pp): The unit of a difference between two percentages. 98.7 % and 97.9 % differ by 0.8 pp, not 0.8 %.
Power: The probability of detecting an effect of a given size if it exists. Small supplier cells here have low power and the index states so rather than concluding no difference.
Precision: Closeness of repeated measurements to each other. Says nothing about accuracy: a precise method can be consistently wrong.
Provenance: How a sample was obtained: buyer-sourced, supplier-supplied or laboratory-retained. A first-class field in this index because it changes the weight of the evidence.
Pharmacopoeial monograph: An official specification and method for a named substance. Exists for oxytocin, desmopressin, gonadorelin, leuprolide, triptorelin and glucagon among the compounds here.
Partial: A verification status: a measurement the compound requires is missing — a metal determination on a complex, an anomeric ratio on NAD+.
Purity only: A verification status: no identity confirmation was ordered. The record describes homogeneity and does not establish what the material is.
Particulate, sub-visible: Particles below the visible threshold, counted by light obscuration under USP <788>. Not measured anywhere in this index.
Photostability: Resistance to light. Tryptophan-containing peptides and the quinolinium adjuncts degrade in clear glass; amber glass is the mitigation.