Glossary
Plain-language definitions of the storage, handling and analytical terms used across Peptide Handling Guide.
Definitions of terms used across the guides. Each entry links to the guide where the term is explained in context.
A
- Aggregation
- Peptide molecules sticking together into dimers, oligomers or visible particles. Driven by hydrophobic contacts, concentration, temperature, agitation and freezing stress. Read the guide on Aggregation
- Aliquot
- A single-use portion split from a larger stock so that the rest is never warmed, opened or contaminated by repeated withdrawals. Read the guide on Aliquot
- Amber glass
- Glass containing iron and sulfur compounds that absorbs most ultraviolet and short-wavelength visible light. Used for light-sensitive material. Read the guide on Amber glass
- Area percent
- The share of a chromatogram's total peak area under the main peak. It is how HPLC purity is usually reported, and it only counts what the detector can see. Read the guide on Area percent
- Asp-Gly site
- An aspartic acid followed by glycine. The small glycine side chain lets the backbone form a succinimide ring easily, so these sites isomerize faster than most. Read the guide on Asp-Gly site
B
- Batch record
- The production record for one manufactured lot: materials, steps, equipment and in-process results. Read the guide on Batch record
C
- Certificate of analysis (COA)
- A document reporting test results for a specific lot, such as identity by mass spectrometry and purity by HPLC, signed by the responsible laboratory. Read the guide on Certificate of analysis (COA)
- Chain of custody
- A record of every hand-off of a sample, showing who held it, when and under what conditions. Read the guide on Chain of custody
- Cold chain
- The unbroken series of temperature-controlled storage and transport steps between manufacture and use. Read the guide on Cold chain
- Counterion
- The ion paired with a charged peptide in the solid, typically trifluoroacetate (TFA) or acetate after purification. It adds weight that is not peptide. Read the guide on Counterion
- Cryoprotectant
- An additive, such as a sugar or glycerol, that protects molecules from freezing stress. Read the guide on Cryoprotectant
D
- Data logger
- An electronic device that records temperature at set intervals so excursions can be detected after the fact. Read the guide on Data logger
- Deamidation
- Loss of the amide group from asparagine or glutamine side chains, forming aspartate, isoaspartate or glutamate. Faster at neutral to basic pH and higher temperature. Read the guide on Deamidation
- Desiccant
- A drying agent, such as silica gel or molecular sieve, kept with dry material to absorb moisture. Read the guide on Desiccant
E
- Electrospray ionization (ESI)
- A mass spectrometry ionization method that sprays a solution into charged droplets, producing multiply charged peptide ions. Read the guide on Electrospray ionization (ESI)
- Equilibrate
- Let a cold container reach room temperature before opening it, so moisture does not condense on the contents. Read the guide on Equilibrate
- Excursion
- Any period when material is outside its specified temperature range. Read the guide on Excursion
F
- Freeze-concentration
- As water freezes into ice, solutes concentrate in the remaining liquid, which can shift pH and drive aggregation. Read the guide on Freeze-concentration
H
- Headspace
- The gas above the contents of a sealed vial. Its oxygen and moisture react with the material over time. Read the guide on Headspace
- HPLC
- High-performance liquid chromatography. Pumps a sample through a packed column and separates components by how they interact with it. Read the guide on HPLC
- Hygroscopic
- Readily absorbing water from the air. Most lyophilized peptides are hygroscopic. Read the guide on Hygroscopic
I
- Inert-gas overlay
- Replacing the air above a sample with dry nitrogen or argon to reduce oxidation and moisture uptake. Read the guide on Inert-gas overlay
- Isoaspartate
- An aspartate linked through its side-chain carboxyl, created when a succinimide intermediate reopens. It changes the backbone and often the activity. Read the guide on Isoaspartate
L
- Lot (batch) number
- The identifier that ties a vial to one manufacturing run and its test results. Read the guide on Lot (batch) number
- Low-binding tube
- A plastic tube with a surface treated or formulated to reduce adsorption of peptides and proteins. Read the guide on Low-binding tube
- Lyophilization
- Freeze-drying: freezing a solution, then removing the ice by sublimation under vacuum and the remaining bound water by gentle heating. Read the guide on Lyophilization
M
- MALDI
- Matrix-assisted laser desorption/ionization. A mass spectrometry method that mostly produces singly charged ions from a sample mixed with a light-absorbing matrix. Read the guide on MALDI
- Monoisotopic mass
- The mass of a molecule made only of the most abundant isotope of each element. Mass spectrometers report it for small peptides. Read the guide on Monoisotopic mass
N
- Net peptide content
- The fraction of a powder's weight that is actually peptide, after water and counterions are accounted for. Often 60–90% for purified synthetic peptides. Read the guide on Net peptide content
O
- Oxidation
- Reaction with oxygen or reactive oxygen species. Methionine, cysteine, tryptophan, histidine and tyrosine are the residues most affected. Read the guide on Oxidation
P
- Photodegradation
- Chemical change caused by absorbed light, mainly ultraviolet, often through aromatic residues and photosensitized oxidation. Read the guide on Photodegradation
- Purity
- For peptides, usually the HPLC area percent of the target peptide among UV-absorbing components. It is not the same as peptide content. Read the guide on Purity
R
- Residual moisture
- Water remaining in a lyophilized solid, measured by Karl Fischer titration or loss on drying. Read the guide on Residual moisture
- Retention time
- How long a component takes to pass through an HPLC column under set conditions. Read the guide on Retention time
- Reversed-phase (RP)
- An HPLC mode with a hydrophobic column and a water-to-organic gradient. The standard method for peptide purity. Read the guide on Reversed-phase (RP)
S
- Succinimide
- A five-membered ring intermediate formed at Asn and Asp residues on the way to deamidation or isomerization. Read the guide on Succinimide
T
- TFA (trifluoroacetic acid)
- An acid used in peptide synthesis and HPLC purification that often remains as a counterion in the final powder. Read the guide on TFA (trifluoroacetic acid)
- Thaw cycle
- One round of warming frozen material above its storage temperature and refreezing it, whether or not the tube was opened. Read the guide on Thaw cycle
U
- Use-by date
- The date after which a prepared solution or aliquot should not be used, set from stability data or a conservative internal rule. Read the guide on Use-by date
W
- Water activity
- How available the water in a material is to take part in reactions. In dry solids it rises with humidity and speeds degradation. Read the guide on Water activity