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Research glossary

The terms that appear on a product record, a chromatogram or a certificate of analysis, defined in plain language. Each definition explains what a word means and what it does not cover. A purity figure and a net peptide content figure answer different questions about the same vial.

30 terms

6 groupings

Definitions only

What is peptide?: A short chain of amino acids joined by peptide bonds, conventionally fewer than about fifty residues; longer chains are usually called proteins. The number, identity and order of the residues determine the molecule’s mass, charge and solubility, and therefore how it behaves in an analytical system.

What the glossary covers

Molecular basics5 terms: What a peptide is and the properties that identify one.
Synthesis and formulation5 terms: How research peptides are made and what ends up in the vial besides peptide.
Analysis and testing10 terms: The instruments and figures behind a purity number.
Documentation and standards3 terms: The paperwork that ties a result to a specific quantity of material.
Research methods5 terms: Terms used to describe where and how an observation was made.
Stability and storage2 terms: Concepts used when material changes over time.

A

AgonistResearch methods: A molecule that binds a receptor and produces a measurable response in the assay system, described by potency and by efficacy relative to a reference compound. A partial agonist produces a submaximal response even when binding is saturated. Both terms are defined by the measurement, not by any outcome.; See alsoAntagonist Receptor binding
Amino acidMolecular basics: The building block of peptides and proteins. Each amino acid carries an amine group, a carboxyl group and a distinguishing side chain that sets its size, charge and polarity. Twenty proteinogenic amino acids occur in most biological systems; synthetic peptides may also incorporate modified or non-natural residues.; See alsoPeptide bond Amino acid sequence
Amino acid sequenceMolecular basics: The order of residues along a chain, written from the N-terminus to the C-terminus using one- or three-letter codes. The sequence is the primary identity of the material: two samples with the same mass but different sequences are different compounds and are documented separately.; See alsoPeptide Molecular weight Mass spectrometry
AntagonistResearch methods: A molecule that binds a receptor without producing a response and reduces the response to an agonist in the same system. Competitive antagonists occupy the agonist binding site and can be displaced by raising agonist concentration; non-competitive antagonists act elsewhere and are not overcome that way.; See alsoAgonist Receptor binding
AssayAnalysis and testing: A defined analytical or biological procedure that measures one property of a sample: identity, concentration, purity or binding. An assay result is only interpretable with its conditions attached: the method, instrument, reference standard and acceptance criteria are all part of what was reported.; See alsoReference standard In vitro Receptor binding

C

Certificate of analysisCOADocumentation and standards: The document a laboratory issues for one specific lot, listing the tests performed, the methods used, the results obtained and the date of testing. A certificate applies only to the lot identified on it, which is why certificates are matched to lot numbers rather than to a product in general.; See alsoLot Purity ISO/IEC 17025
ChromatogramAnalysis and testing: The plot a chromatography detector produces: signal intensity against elution time. Each peak corresponds to a component leaving the column, its position records when that component eluted, and its area is proportional to the amount detected. Purity figures are calculated from the relative areas of those peaks.; See alsoHigh-performance liquid chromatography Retention time Purity
CounterionSynthesis and formulation: The charged species paired with a peptide’s ionisable groups in the dried salt, most often trifluoroacetate or acetate. Counterions add mass without adding peptide, so their identity affects net peptide content, and they can influence solubility and behaviour in sensitive cell-culture systems.; See alsoTrifluoroacetic acid Net peptide content

E

EndotoxinAnalysis and testing: Lipopolysaccharide fragments from the outer membrane of Gram-negative bacteria. They are heat-stable, survive many purification steps and can confound cell-based experiments at very low concentrations. Levels are expressed in endotoxin units per milligram and measured by limulus amebocyte lysate or recombinant factor C methods.; See alsoAssay Certificate of analysis

H

Half-lifeStability and storage: The time taken for a measured quantity to fall to half its initial value in a defined system: a compound degrading in buffer during an in vitro stability study, for example. A half-life is only interpretable alongside the system, temperature and matrix in which it was measured.; See alsoStorage stability In vitro
High-performance liquid chromatographyHPLCAnalysis and testing: A separation technique that pumps a sample through a packed column under high pressure; components emerge at different times according to how strongly they interact with the stationary phase. Reversed-phase HPLC, using a nonpolar column and a water–acetonitrile gradient, is the standard purity method for peptides.; See alsoChromatogram Retention time Purity

I

In vitroResearch methods: Latin for “in glass”: work carried out outside a living organism, in controlled systems such as cell cultures, isolated tissue preparations, purified enzymes or binding assays. An in vitro result describes what happened in that defined system and does not by itself establish what occurs in a whole organism.; See alsoIn vivo Assay Receptor binding
In vivoResearch methods: Work carried out in a living organism, typically an animal model in preclinical research. In vivo systems introduce distribution, metabolism and clearance, which isolated preparations do not, so in vivo and in vitro observations for the same compound frequently differ and are reported separately.; See alsoIn vitro Half-life
ISO/IEC 17025Documentation and standards: The international standard for the competence of testing and calibration laboratories, covering method validation, equipment calibration, personnel competence and traceability of results. Accreditation is granted by an accreditation body for a defined scope of methods, so it is meaningful only for the methods within that scope.; See alsoCertificate of analysis Reference standard

L

LC-MSLiquid chromatography–mass spectrometryAnalysis and testing: Liquid chromatography coupled to a mass spectrometer, so components are separated in time and then measured by mass as they elute. Linking a chromatographic peak to a specific measured mass is why identity confirmation and impurity characterisation are normally reported from LC-MS rather than chromatography alone.; See alsoHigh-performance liquid chromatography Mass spectrometry Certificate of analysis
LotBatchDocumentation and standards: A quantity of material produced in a single run under uniform conditions and given a unique identifier. Analytical results, certificates and stability information apply to a specific lot, so the lot number printed on a vial is the link between the physical material and its documentation.; See alsoCertificate of analysis Storage stability
LyophilisationFreeze-dryingSynthesis and formulation: Removal of water from a frozen solution under vacuum by sublimation, leaving a dry cake or powder. Peptides are commonly supplied lyophilised because a dry solid is more stable in transit and storage than a solution, and because water removed from the matrix is no longer available for hydrolysis.; See alsoStorage stability Net peptide content

M

Mass spectrometryMSAnalysis and testing: A technique that ionises a sample and separates the ions by mass-to-charge ratio, producing a spectrum that reports measured molecular mass. For peptides it confirms that the observed mass matches the mass calculated from the stated sequence, and can reveal truncations, deletions or modifications.; See alsoMolecular weight LC-MS Amino acid sequence
Molecular weightMWMolecular basics: The mass of one molecule, expressed in daltons or grams per mole and calculated from the atomic composition implied by the sequence. Analytical records distinguish the monoisotopic mass, computed from the most abundant isotopes, from the average mass taken across the natural isotope distribution.; See alsoMass spectrometry Amino acid sequence

N

Net peptide contentNPCAnalysis and testing: The fraction of a lyophilised material that is peptide once counterions, residual water and residual solvent are excluded, typically established by amino acid analysis or nitrogen determination. A material can show high chromatographic purity and a materially lower net peptide content, so both figures are reported.; See alsoPurity Counterion Trifluoroacetic acid

P

PeptideMolecular basics: A short chain of amino acids joined by peptide bonds, conventionally fewer than about fifty residues; longer chains are usually called proteins. The number, identity and order of the residues determine the molecule’s mass, charge and solubility, and therefore how it behaves in an analytical system.; See alsoAmino acid Peptide bond Amino acid sequence
Peptide bondMolecular basics: The covalent amide link formed when the carboxyl group of one amino acid condenses with the amine group of the next, releasing a molecule of water. The bond is planar and comparatively rigid, which constrains the backbone geometries a peptide chain can adopt in solution.; See alsoPeptide Amino acid
PurityChromatographic purityAnalysis and testing: The proportion of a sample attributable to the target compound, usually calculated as the target peak area divided by total peak area in an HPLC chromatogram. Because it is area-based, purity describes composition relative to what the method detects, not how much peptide the vial contains.; See alsoNet peptide content Chromatogram Certificate of analysis

R

Receptor bindingResearch methods: The reversible association of a molecule with a specific protein target, characterised in vitro by measurements such as the dissociation constant or by competition against a labelled reference ligand. Binding describes an interaction under the assay conditions used; it does not by itself describe a downstream consequence.; See alsoAgonist Antagonist Assay
Reference standardAnalysis and testing: A well-characterised material of known identity and purity used to calibrate a method or to confirm a sample’s identity by comparison. Results reported against a reference standard are traceable to that material, so the standard used is normally named or coded in the analytical record.; See alsoAssay Retention time ISO/IEC 17025
Residual solventSynthesis and formulation: Organic solvent left over from synthesis, cleavage or purification. Acetonitrile, dichloromethane and diethyl ether are typical examples. Levels are quantified by gas chromatography, often headspace GC, and reported against recognised limits because solvents add mass and can interfere with downstream analytical work.; See alsoSolid-phase peptide synthesis Net peptide content
Retention timeRTAnalysis and testing: The interval between a sample entering the chromatography column and its peak reaching the detector. Under fixed method conditions it is reproducible and characteristic of a compound, so it is used to support identity by comparison with a reference standard. Changing column, gradient or temperature changes retention time.; See alsoChromatogram Reference standard High-performance liquid chromatography

S

Solid-phase peptide synthesisSPPSSynthesis and formulation: The standard route to research peptides: the chain is assembled one protected residue at a time on an insoluble resin support, then cleaved from the resin and purified. Incomplete coupling and side reactions during assembly are the origin of most sequence-related impurities seen later in analysis.; See alsoHigh-performance liquid chromatography Purity Residual solvent
Storage stabilityStability and storage: How well a material retains its identity and purity over time under stated conditions. Stability studies hold samples at a defined temperature, humidity and light exposure and re-test them at intervals. A stability statement applies only to the conditions tested, which is why storage conditions always accompany it.; See alsoLyophilisation Lot Half-life

T

Trifluoroacetic acidTFASynthesis and formulation: The ion-pairing additive used in most reversed-phase peptide purification. It commonly remains in the finished solid as the trifluoroacetate counterion, where it adds mass, lowers net peptide content and is documented as a residue because it can interfere with some cell-based assay systems.; See alsoCounterion High-performance liquid chromatography Net peptide content

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