This glossary defines 55 terms you will meet when buying, documenting and handling research peptides — from peptide-bond basics through HPLC purity, mass-spectrometry identity and certificates of analysis, to lyophilization, storage and supplier verification. Definitions are written in plain English for students, laboratory staff and research buyers in Canada and elsewhere. Every term has its own link, so you can cite or bookmark a single definition.
Peptide chemistry & structure
- Peptide #
- A short chain of amino acids joined by peptide bonds. Peptides are generally distinguished from proteins by length: chains of roughly 2–50 amino acids are called peptides, while longer chains that fold into complex structures are called proteins.
- Amino acid #
- The building block of peptides and proteins. Each amino acid shares a common backbone and differs by its side chain, which determines its chemical behaviour. Twenty standard amino acids occur in natural proteins; synthetic peptides may also use modified or non-natural residues.
- Residue #
- A single amino acid unit within a peptide chain, so called because it is what remains of the amino acid after water is released during peptide-bond formation. A “31-residue peptide” contains 31 linked amino acids.
- Peptide bond #
- The amide bond formed between the carboxyl group of one amino acid and the amino group of the next. The sequence of peptide bonds forms the backbone of every peptide.
- Sequence #
- The ordered list of amino acids in a peptide, written from the N-terminus to the C-terminus using one-letter or three-letter codes. The sequence defines the peptide’s identity; two peptides with the same name but different sequences are different compounds.
- N-terminus #
- The end of a peptide chain with a free amino group, by convention the start of the written sequence. It may carry modifications such as acetylation.
- C-terminus #
- The end of a peptide chain with a free carboxyl group, by convention the end of the written sequence. Many synthetic peptides are C-terminally amidated.
- Solid-phase peptide synthesis (SPPS) #
- The standard laboratory method for making synthetic peptides: the chain is assembled one amino acid at a time while anchored to an insoluble resin, then cleaved from the resin and purified. Most commercial research peptides are produced this way.
- Fmoc chemistry #
- The most common SPPS strategy, named for the fluorenylmethyloxycarbonyl protecting group that temporarily blocks each amino acid’s amino group during coupling. Milder than the older Boc approach, it avoids repeated strong-acid treatment.
- Protecting group #
- A chemical group attached during synthesis to stop an amino acid’s reactive side chain or terminus from reacting at the wrong step. Protecting groups are removed (deprotected) at the end; incomplete removal is one source of synthesis impurities.
- Crude peptide #
- The unpurified product of synthesis, containing the target sequence alongside deletion sequences, truncated chains and other by-products. Purification, usually by preparative HPLC, separates the target peptide from these impurities.
- Deletion sequence #
- A synthesis by-product missing one or more amino acids because a coupling step did not complete. Deletion sequences are close relatives of the target peptide, which is why chromatographic purification and purity testing matter.
- Disulfide bridge #
- A covalent bond between the sulfur atoms of two cysteine residues that constrains a peptide’s shape. Peptides with disulfide bridges (or head-to-tail cyclization) are called cyclic peptides; forming the correct bridge is a distinct, verifiable synthesis step.
- Acetylation and amidation #
- Common terminal modifications in synthetic peptides: an acetyl group capping the N-terminus and/or an amide replacing the free acid at the C-terminus. They alter charge and stability and are part of the compound’s defined structure, so a certificate should reflect the modified mass.
- Peptide analog #
- A peptide deliberately modified from a reference sequence — by substituting, adding or removing residues or adding chemical groups — to change its properties. Analogs are distinct compounds and should be labelled and documented as such.
- Molecular weight (average vs monoisotopic) #
- The mass of a peptide calculated from its formula. Average mass uses natural isotope abundances; monoisotopic mass uses the lightest isotopes and is what high-resolution mass spectrometry reports. Comparing the observed mass with the calculated mass confirms identity.
Analytical testing & quality documentation
- HPLC (high-performance liquid chromatography) #
- The workhorse technique for assessing peptide purity. The sample is pumped through a column that separates components by their chemical properties; a detector records each component as a peak. Purity is reported as the main peak’s share of total peak area.Related: HPLC testing guide
- Reverse-phase HPLC (RP-HPLC) #
- The HPLC mode used for most peptide analysis: a nonpolar column retains components by hydrophobicity while a water–acetonitrile gradient elutes them. Small differences in sequence or modification shift retention enough to separate target from impurities.
- Chromatogram #
- The output trace of an HPLC run: detector signal versus time. A clean chromatogram shows one dominant peak with a flat baseline; shoulders or extra peaks indicate related impurities worth reading past the headline purity number.
- Retention time #
- How long a compound takes to pass through the HPLC column under a given method. It is reproducible only within the same method, so retention times from different labs or gradients are not directly comparable.
- Peak-area purity #
- The percentage of total chromatogram peak area contributed by the main peak. It is method-dependent — column, gradient and detection wavelength all influence it — and it measures chromatographic purity, not identity and not net content.
- UV detection at 214 nm / 220 nm #
- Peptide bonds absorb ultraviolet light most strongly around 210–220 nm, so purity chromatograms typically monitor these wavelengths. Detection at 254/280 nm sees mainly aromatic residues and can under-report impurities that lack them.
- Mass spectrometry (MS) #
- The identity test: it measures molecular mass, which is compared with the mass calculated from the stated sequence. A matching mass confirms composition; it cannot quantify impurities well and cannot distinguish isomers of identical mass.
- ESI-MS and MALDI-TOF #
- The two ionization techniques most used for peptides. Electrospray (ESI) produces multiply charged ions and pairs well with LC systems; MALDI-TOF ionizes samples from a solid matrix and reads singly charged ions. Either can confirm identity.
- Certificate of analysis (COA) #
- The document reporting what testing found for a specific batch: identity, purity, and any additional assays, tied to a lot number. A COA applies only to the batch it names; reading one well is a basic skill for any research buyer.Related: How to read a peptide COA · Lab testing & COAs
- Batch / lot number #
- The identifier linking a physical vial to its production run and test records. Matching the number printed on the vial to the number on the COA is what makes documentation meaningful.
- Verification key #
- A code some independent laboratories print on their reports that lets anyone confirm the document against the laboratory’s own records online, protecting against altered or fabricated certificates.Related: Lab testing & verification
- Identity vs purity vs content #
- Three different claims: identity (is it the right molecule — answered by MS), purity (how much of the detected material is the main peak — answered by HPLC) and content (how much actual peptide is in the vial — answered by net peptide content analysis). A thorough quality picture needs all three.
- Net peptide content #
- The fraction of a lyophilized powder’s weight that is actually peptide, as opposed to bound water and counter-ions. Often 70–90%. Molar calculations based on gross vial weight instead of net content are a common source of concentration error.
- Water content (Karl Fischer) #
- Residual moisture in a lyophilized product, commonly measured by Karl Fischer titration. Lyophilized peptides are hygroscopic, and water adds weight without adding peptide.
- Counter-ion (TFA / acetate salt) #
- The charged species paired with a peptide after purification. RP-HPLC purification with trifluoroacetic acid typically yields TFA salts; acetate is a common alternative. Counter-ions contribute weight and can matter in sensitive cell-based work.
- Endotoxin testing #
- An assay (classically LAL) for bacterial endotoxins. It is not part of standard research-grade peptide release testing; laboratories using sensitive biological systems typically assess and control endotoxin themselves.
- Reference standard #
- A well-characterized sample of a compound used to calibrate or compare analytical measurements. Running a known standard alongside a test sample anchors retention time and mass assignments.
Forms, storage & handling
- Lyophilization (freeze-drying) #
- Removing water from a frozen solution under vacuum so it sublimes, leaving a dry powder or cake. Lyophilized peptides are far more stable than solutions, which is why research peptides ship as dry vials.Related: Peptide storage guide
- Lyophilized cake #
- The porous solid left in a vial after freeze-drying. An intact cake that reconstitutes clearly is a quick visual quality check; a melted-looking, discoloured or displaced cake suggests moisture exposure or heat history.
- Reconstitution #
- Dissolving a lyophilized peptide in a suitable solvent before laboratory use. Solvent choice depends on the peptide’s properties; gentle handling (no vortexing of foaming-prone solutions) preserves integrity. Reconstituted solutions are much less stable than powder.
- Bacteriostatic water #
- Sterile water containing 0.9% benzyl alcohol to inhibit bacterial growth in multi-use laboratory containers. One of several common reconstitution diluents for in-vitro work.
- Solubility #
- How readily a peptide dissolves in a given solvent, largely determined by its charged and hydrophobic residues. Poor solubility is a property, not necessarily a defect; hydrophobic sequences may need organic co-solvent.
- Aliquot #
- A single-use portion of a reconstituted stock, divided out so the remainder is not repeatedly warmed, opened or refrozen. Aliquoting is the standard defence against freeze–thaw degradation.
- Freeze–thaw cycle #
- One round of freezing and thawing a solution. Each cycle stresses dissolved peptides through ice-crystal formation and concentration effects; repeated cycles measurably degrade many sequences.
- Hygroscopicity #
- The tendency of lyophilized material to absorb atmospheric moisture. It is why vials should reach room temperature before opening (preventing condensation) and be resealed promptly.
- Oxidation and deamidation #
- The two most common chemical degradation routes for stored peptides: methionine, cysteine and tryptophan residues oxidize; asparagine and glutamine residues deamidate. Sequence composition predicts which risk dominates.
- Cold chain #
- Keeping a temperature-sensitive product within its intended temperature range through storage and transport. For lyophilized peptides, brief ambient transit is generally tolerated; long-term storage belongs in a freezer.
- Desiccant #
- A moisture-absorbing material packed alongside moisture-sensitive goods. Silica gel sachets in peptide packaging protect against humidity during transit and storage.
- Stability #
- How well a compound retains its identity and purity over time under stated conditions. Stability depends on form (powder vs solution), temperature, light, moisture and sequence; test results describe the material at testing time, not indefinitely.
Sourcing, compliance & documentation
- Research use only (RUO) #
- A supply designation meaning products are sold strictly as laboratory reagents for in-vitro research — not drugs, supplements or cosmetics, and not for human or veterinary use of any kind. RUO suppliers do not provide dosing or administration guidance.Related: What research-use-only means in practice
- In-vitro research #
- Literally “in glass”: experiments performed with cells, tissues or biochemical systems outside a living organism — binding assays, enzyme kinetics, cell-culture studies and analytical method development are typical examples.
- Independent (third-party) testing #
- Analysis performed by a laboratory unaffiliated with the manufacturer or seller. Independence plus verifiable reports (task numbers, verification keys) is what makes a purity claim checkable rather than promotional.Related: Lab testing & COAs
- Traceability #
- The ability to connect a specific vial to its batch records: lot number on the label, matching COA, and a supplier who can produce documentation for earlier batches on request.
- Supplier verification #
- The checks a buyer can run before ordering: a real business address and contact route, published independent test reports matched to batches, a written returns policy, and consistent research-use-only positioning.Related: Choosing a Canadian peptide supplier
- Safety data sheet (SDS) #
- A standardized document describing a substance’s hazards, safe handling, storage and disposal for workplace safety purposes. Laboratories commonly require an SDS on file for materials in use.
- Research-grade vs GMP-grade #
- GMP (Good Manufacturing Practice) is the pharmaceutical production standard required for clinical materials. Research-grade peptides are manufactured and tested for laboratory use, not under full GMP; a research supplier should not claim GMP status it does not have.
- Xpresspost / tracked domestic shipping #
- Shipping entirely within one country with end-to-end tracking. For Canadian laboratories, domestic fulfilment avoids customs holds and brokerage fees that affect imported research materials.Related: Shipping across Canada
- Customs hold and brokerage #
- Delays and fees that can apply when research materials cross a border: packages may be inspected, assessed duties or handling charges, and sit in bonded storage — all time a temperature- and project-sensitive material spends in limbo.
- Price per milligram #
- A normalized way to compare peptide offers: vial price divided by labelled quantity. Only meaningful alongside documentation quality — purity, identity confirmation and net content determine what a milligram actually delivers.
Citing or linking to this glossary
This glossary is free to reference. Educators, librarians and writers are welcome to link to the whole page or to a single definition using its #term link.
Research Peptide Glossary. Pure Peptides Canada, Toronto. https://purepeptidescanada.com/peptide-glossary/ (accessed [date]).
Spotted an error or a missing term? Tell us — corrections are reviewed by our team and this page is updated in place.
Research use only. Everything on this page describes laboratory chemistry, analytics and logistics. Research peptides are laboratory reagents: they are not drugs, supplements or cosmetics, are not approved for human or veterinary use, and nothing here is dosing, administration or medical guidance.
