Glossary
Short, practical definitions for the vocabulary used in peptide sourcing, analytics and logistics. Each entry links to the guide that covers it in depth.
Analytical & quality
- HPLC
- High-performance liquid chromatography. Separates components of a sample and reports area percentages at a chosen wavelength; the basis of most peptide purity figures. Read more
- Chromatogram
- The plotted output of an HPLC run. Look at peak shape, baseline and impurity peaks, not only the main-peak percentage. Read more
- Mass spectrometry (MS)
- Measures molecular mass to confirm identity. An MS result supports “this is the right molecule”; it does not by itself prove purity. Read more
- Sequence
- The order of amino acid residues from the N-terminus to the C-terminus, written in one-letter code. Direction, terminal groups and modifications are part of the identity, not decoration. Read more
- Residue mass
- The mass of an amino acid after it has lost water forming the peptide bond. A peptide's free-acid mass is the sum of residue masses plus one water molecule. Read more
- Monoisotopic mass
- Mass calculated from the single most abundant isotope of each element. It differs from average mass, and the gap grows with molecule size. Read more
- b and y ions
- The two backbone fragment series used to read a peptide sequence in tandem MS. A b ion is an N-terminal fragment plus a proton; a y ion is a C-terminal fragment plus water and a proton. Read more
- Sequence coverage
- The share of backbone positions supported by observed fragment ions in an MS/MS experiment. A high percentage can still hide an unconfirmed stretch in the middle of the sequence. Read more
- Isobaric residues
- Different residues with the same mass — leucine and isoleucine most notably. Mass alone cannot distinguish them, and standard CID fragmentation usually cannot either. Read more
- Stability study
- A protocol that measures defined attributes over time at stated storage conditions. Real-time data support a shelf life; accelerated data describe degradation pathways. Read more
- Purity vs assay
- Purity is the share of the main peak by a given method. Assay is the quantity of the target compound measured against a standard. They are not interchangeable. Read more
- Related impurity
- A molecule close in structure to the target — a deletion, truncation or oxidation product. Its profile matters more than a single purity number. Read more
- Karl Fischer titration
- The standard method for water content in a lyophilized cake. Residual moisture affects stability and cake integrity. Read more
- Net peptide content
- The mass fraction of a powder that is peptide, excluding counter-ion, water and residual salts. Different from HPLC purity. Read more
- Fill weight
- The total powder mass in a vial. It includes the counter-ion and residual moisture, so it is not the mass of peptide. Read more
- Amino-acid analysis (AAA)
- Hydrolysis of a sample to free amino acids, followed by separation and quantification. A primary method for peptide content. Read more
- Mass balance
- Estimating peptide content by subtracting water, counter-ion and residual solvents from 100%. Only as good as the subtracted assays. Read more
- Extinction coefficient
- The molar absorptivity used to convert an absorbance reading into a concentration (M⁻¹cm⁻¹). For peptides it is estimated from Trp, Tyr and cystine content. Read more
- Beer–Lambert law
- A = ε·c·l: absorbance is proportional to concentration and path length. It holds only for dilute solutions without scattering. Read more
- BCA assay
- A colorimetric protein/peptide assay based on copper reduction. Sequence-dependent and incompatible with reducing agents such as DTT. Read more
- qNMR
- Quantitative nuclear magnetic resonance against an internal standard. A primary concentration method when the compound is soluble and a signal is resolvable. Read more
- Reference standard
- A lot with an assigned value and a stated uncertainty, characterised by an independent programme and used to calibrate working standards or settle disputes. Read more
- Working standard
- A lot qualified in-house against a reference standard, used for routine system suitability and calibration. It carries the assigned value forward, and needs its own records. Read more
- System suitability
- The injections and checks run before a sample sequence to show the system is fit that day: resolution, tailing, repeatability and carryover. Read more
- Dwell volume
- The liquid volume between the gradient mixer and the column. It delays the programmed gradient, and differences between instruments shift retention on transfer. Read more
- End-capping
- A treatment that blocks residual silanol groups on a silica column. Fewer free silanols means less tailing for basic peptides at low pH. Read more
- ICP-MS
- Inductively coupled plasma mass spectrometry. Measures total element concentration at trace levels; sample digestion decides whether the result is complete. Read more
- ICH Q3D
- The guideline that classifies elemental impurities by toxicity and sets permitted daily exposures. For a research peptide without a dose, it informs limits rather than fixing them. Read more
- PDE (permitted daily exposure)
- A dose-based limit for an elemental impurity. It cannot be converted to a ppm specification without a defined daily dose. Read more
- Speciation
- The chemical form of an element — oxidation state or bound species. Total element analysis by ICP-MS does not report speciation. Read more
- COA (certificate of analysis)
- The lot-specific document stating test methods, results and specification limits. It must reference the batch it belongs to. Read more
- Retention sample
- Material held back from a lot for later comparison or retest. Ask for it contractually; it is the cheapest dispute tool you have. Read more
- Specification
- The written set of limits and methods a lot must meet. A product name is not a specification. Read more
- OOS (out of specification)
- A result outside the agreed limits. The response — rejection, investigation or retest — should be defined before you order. Read more
- Preparative HPLC
- Chromatography run to recover material rather than to measure it. Overloaded columns trade resolution for throughput, and the fraction cut sets purity and yield together. Read more
- Salt conversion
- Exchanging the counter-ion associated with a peptide — commonly TFA for acetate — without changing the sequence. Each exchanged site shifts salt mass by roughly 54 Da. Read more
- SEC (size-exclusion chromatography)
- Separation by hydrodynamic size. Good for stable oligomers; dilution on the column can dissociate weak aggregates. Read more
- DLS (dynamic light scattering)
- Derives a hydrodynamic radius from scattered-light fluctuations. Intensity-weighted, so a few large species can dominate the result. Read more
- AUC (analytical ultracentrifugation)
- Sedimentation analysis in a centrifugal field. Resolves species in solution without a column, but is slow and specialist. Read more
Manufacturing
- SPPS
- Solid-phase peptide synthesis. The peptide is built stepwise on a resin, then cleaved and purified. Scale and resin choice drive impurity profiles. Read more
- Resin
- The solid support for SPPS. A change of resin lot can shift coupling efficiency and the impurity profile. Read more
- Cleavage and deprotection
- The step that releases the peptide from the resin and removes side-chain protecting groups. Incomplete cleavage leaves modified by-products. Read more
- Purification
- Usually preparative HPLC. Gradient and fraction cutting determine which impurities survive into the final lot. Read more
- Lyophilization
- Freeze-drying. Removes water from the purified solution to give a stable cake; the cycle affects moisture and cake structure. Read more
- Counter-ion
- The ion paired with the peptide — commonly acetate or TFA. It changes mass, pH and solubility, and should be stated on the specification. Read more
- Batch / lot
- A single production run with one batch number. Certificates and retention samples attach to the lot, not to the product name. Read more
- Scale-up
- Moving a synthesis from grams to tens or hundreds of grams. Coupling and purification behaviour change; a successful small run does not guarantee the large one. Read more
Sourcing & commercial
- MOQ
- Minimum order quantity. Often set per SKU and per packaging format rather than per order. Read more
- Tier pricing
- Unit price steps tied to quantity. Confirm whether tiers apply per SKU or across a mixed order. Read more
- RFQ
- Request for quotation. A useful RFQ lists SKU, strength, quantity, destination and documentation requirements. Read more
- Incoterms
- Standard trade terms (EXW, FOB, CIF, DDP) that allocate cost and risk. Name the term and the place in the contract. Read more
- HS code
- Customs classification code. The code determines duty and whether an import permit is required at destination. Read more
- T/T (telegraphic transfer)
- A bank wire payment. Common for first orders; the protection it offers depends on what the payment is conditioned on, not on the transfer itself. Read more
- Letter of credit (L/C)
- A bank undertaking to pay against compliant documents. It protects both sides only if the document set is written precisely and checked strictly. Read more
- Beneficiary
- The account holder receiving a payment. It must match the contracting entity; mismatches are the most common sign of payment fraud in this trade. Read more
- Escrow
- Funds held by a third party and released when agreed milestones are met. Useful for mid-size orders where neither full prepayment nor credit terms is acceptable. Read more
- Change control
- The contractual process for notifying and approving changes to process, site or specification. Its absence is a common source of silent drift. Read more
- OEM
- Original equipment manufacturer. Here: supply under the buyer’s brand, with agreed label and documentation. Read more
- Private label
- A product sold under the buyer’s brand rather than the manufacturer’s. Label rules and registrations differ by market. Read more
- Qualification
- The pre-order process of checking documentation, samples and references before committing to a supplier. Read more
- Dual sourcing
- Qualifying a second supplier for a critical SKU to reduce single-source risk. Requires comparable specifications. Read more
- Retest date
- The date to which a supplier warrants the specification, after which the lot must be re-analysed before use. Not the same as an expiry date. Read more
- Safety stock
- Inventory held to cover lead-time variability rather than average demand. Scales with the standard deviation of lead time, not with the mean. Read more
Handling & logistics
- Lyophilized powder
- Freeze-dried peptide, typically a porous cake or powder in a sealed vial. More stable in transit than a solution. Read more
- Reconstitution
- Dissolving lyophilized peptide in a suitable laboratory solvent. Concentration is calculated from the measured mass, not assumed. Read more
- Freeze–thaw cycle
- Repeated freezing and thawing of a solution. Aliquot before freezing to limit damage. Read more
- Cold chain
- Temperature-controlled handling from dispatch to delivery. Required for sensitive material; overkill for many lyophilized lots on short routes. Read more
- Phase-change pack
- A pack that holds a temperature band during transit. Check it is still within range on arrival. Read more
- Desiccant
- A moisture absorber included in packaging. It manages humidity, not temperature. Read more
- Aggregation
- Non-specific clumping of peptide molecules through hydrophobic and charge interactions. It can reduce soluble recovery without changing the certificate. Read more
- Self-assembly
- Sequence-encoded organisation of peptides into defined structures such as fibrils or gels. A property of the molecule, not a handling error. Read more
- Isoelectric point (pI)
- The pH at which a peptide carries no net charge and is usually least soluble. Buffer away from it rather than relying on water. Read more
- Headspace
- The gas volume above the powder in a vial or pouch. Its oxygen and moisture content drive slow degradation; inert-gas flushing reduces it. Read more
- Customs hold
- Detention of a shipment for inspection or missing documents. Plan for it on time-sensitive orders. Read more
- RUO
- Research use only. A labelling and use restriction: not for human or veterinary use, diagnosis, treatment or cosmetic application. Read more
Research use only. Definitions describe laboratory and commercial practice; they are not medical or regulatory advice.