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Glossary

Terms beginning with R

37 of 238 glossary terms.

Re-equilibration: Returning the column to starting conditions after a gradient. At least ten column volumes; short re-equilibration causes retention drift across a sequence.
Reporting threshold: The area percent below which peaks are not reported. The index uses 0.05 %. Excluded peaks are excluded from the total, so purity is systematically overstated by their sum.
Resolution (R): Separation between two peaks: R = 2(t₂ − t₁)/(w₁ + w₂). R = 1.5 is baseline resolution. The index requires R ≥ 1.20 to the nearest named impurity.
Retention time: Time from injection to peak apex. A property of the compound, the column and the gradient — comparable across laboratories only after gradient normalisation.
Reverse-phase chromatography: Separation on a non-polar stationary phase, typically C18-bonded silica, with a polar mobile phase. Retains by hydrophobic interaction.
Resolving power: A mass spectrometer's ability to separate two close masses, expressed as m/Δm. A quadrupole gives ~1,000; a TOF 20,000–50,000.
Recovered mass: Gross fill × target-compound content / 100. The milligrams of named compound actually obtainable from the vial.
Relative response factor: The detector response of an impurity per unit mass, relative to the parent. Assumed to be 1.00 in almost all purity determinations, and usually is not.
Residual moisture: Water remaining in a lyophilised cake. 1–4 % in well-dried material; 8–13 % for hygroscopic short peptides.
Residual solvent: Process solvent remaining in the product. DMF, DMSO, acetonitrile and dichloromethane are the usual candidates in peptide synthesis. Controlled by ICH Q3C.
Racemisation: Loss of stereochemical purity toward a 50:50 mixture. In stepwise peptide synthesis the practical concern is epimerisation at individual residues.
Regioisomer: An isomer differing in the position of a substituent, for example an acyl group on a different side chain. Mass-identical.
Related substance: A process- or degradation-derived impurity structurally related to the target. The pharmacopoeial term for what a purity method quantifies.
Resin: The insoluble polymer support on which solid-phase synthesis is performed. Loading and swelling behaviour determine achievable purity for difficult sequences.
Recombinant: Produced by expression in a host organism rather than by chemical synthesis. Brings folding, glycosylation and host-cell-protein questions that a purity figure does not address.
Recombinant factor C (rFC): A recombinant alternative to LAL using the cascade's first enzyme. Equivalent sensitivity, no horseshoe crabs.
Regression to the mean: The tendency of an extreme observation to be followed by a less extreme one. Why a retest after a bad result usually looks better regardless of any change.
Repeatability: Precision under identical conditions in one session, same analyst, same instrument. The narrowest kind of precision.
Reproducibility: Precision across laboratories. The index estimates it from paired same-batch comparisons.
Range: The concentration interval over which accuracy, linearity and precision have been demonstrated.
Robustness: A method's tolerance to deliberate small changes in conditions — temperature, pH, organic fraction.
Reference standard: A material of known content used to quantify an analyte. Absent for most research peptides, which is why content is rarely measured.
Retest date: The date by which a material should be re-tested rather than discarded. Distinct from an expiry date and less often stated.
Rule AX-R01: Mass accuracy outside the class limit. Records identity as not established rather than failed, because most instances are calibration problems.
Rule AX-R02: A certificate's declared purity and declared total impurities do not sum to 100 %. A documentation finding: the certificate is not interpretable as written.
Rule AX-R03: A certificate reports a largest single impurity exceeding its total impurities. Arithmetically impossible; a template error.
Rule AX-R04: Repeated round-number purity declarations from one supplier. Requires a pattern of at least three, because one round result is unremarkable.
Rule AX-R05: Declared purity more than 1.5 pp above the median of at least two independent tests on the same lot. The index's most consequential rule.
Rule AX-R06: Recovered mass outside ±10 % of label claim. The rule that fires most often and matters most to anyone buying by the milligram.
Rule AX-R07: Declared water, counter-ion, peptide content and residual do not account for 100 % of mass. Usually an unstated reporting basis.
Rule AX-R08: Endotoxin above the index screening threshold of 5.0 EU/mg. A screening figure, not a pharmacopoeial limit.
Rule AX-R09: Impurity fingerprints matching across suppliers, indicating one bulk under two labels. Not improper; means two results are one measurement.
Rule AX-R10: A supplier-supplied sample reading more than 0.8 pp above buyer-sourced material from the same lot.
Rule AX-R11: Retention time outside the compound window after gradient normalisation. Two thirds of instances are undocumented method differences.
Rule AX-R12: Peak asymmetry above 1.50 or resolution below 1.20 to the nearest impurity. Makes the reported purity a range rather than a number.
Reconstitution: Dissolving a lyophilised cake in diluent. Procedure matters: directing a stream at the cake or shaking can nucleate aggregates that were not in the vial.
Reconstitution clarity: The visual appearance of the reconstituted solution. Recorded verbatim in this index because the descriptive detail is the diagnostic content.