A reference glossary of the terms, units and abbreviations that appear on research peptide labels, Certificates of Analysis and supplier documentation. Definitions are chemical and analytical only.
Units and quantities
- mg (milligram)
- One thousandth of a gram. The standard unit for the gross powder mass in a lyophilized peptide vial.
- mcg / µg (microgram)
- One millionth of a gram; 1 mg = 1000 mcg. Written "mcg" on labels to avoid the µ symbol being misread.
- IU (International Unit)
- A unit of biological activity rather than mass, defined separately for each substance. IU cannot be converted to milligrams without a substance-specific conversion factor.
- mg/mL
- Concentration: milligrams of solute per millilitre of solution. Determined by vial mass divided by solvent volume added.
- g/mol (Da, dalton)
- Molecular weight. A peptide of 1419.5 g/mol has a molecular mass of 1419.5 daltons.
- kDa (kilodalton)
- 1000 daltons. Used for proteins and larger peptides.
Analytical methods
- HPLC
- High-performance liquid chromatography. Separates components of a mixture by their differing affinity for a stationary phase. Reported purity is the main peak's share of total peak area.
- RP-HPLC
- Reversed-phase HPLC, the standard variant for peptides: a nonpolar stationary phase (commonly C18) with a polar mobile phase.
- MS
- Mass spectrometry. Measures mass-to-charge ratio to confirm molecular identity against a theoretical value.
- LC-MS
- Liquid chromatography coupled to mass spectrometry — separation and identification in one run.
- ESI-MS
- Electrospray ionisation mass spectrometry, the usual ionisation method for peptides.
- MALDI-TOF
- Matrix-assisted laser desorption/ionisation with time-of-flight detection. Common for larger peptides and proteins.
- AAA
- Amino acid analysis. Hydrolyses the peptide and quantifies the constituent amino acids; the reference method for net peptide content.
- Retention time (Rt)
- How long a component takes to travel through the HPLC column. Characteristic of a compound under a defined method.
- Area %
- The share of total integrated peak area attributable to one peak. The basis of a reported purity figure.
- Karl Fischer titration
- The standard method for measuring residual water content in a lyophilized powder.
Documentation
- COA (Certificate of Analysis)
- A batch-specific laboratory report giving identity, purity and, where measured, content and residual solvents. See how to read a COA.
- Batch / lot number
- The identifier tying a physical vial to a specific production run and its COA. A COA without a matching lot number on the vial is unverifiable.
- CAS number
- Chemical Abstracts Service registry number — a unique identifier for a chemical substance. Distinct salt forms and complexes have distinct CAS numbers.
- Third-party tested
- Analysis performed by a laboratory independent of the seller and manufacturer.
- Specification vs result
- "≥99%" is a specification (a target). "99.4%" with a chromatogram is a result (a measurement).
Material and form
- Lyophilized
- Freeze-dried. Water removed by sublimation under vacuum, leaving a porous dry cake. Why peptides ship lyophilized.
- Reconstitution
- Dissolving lyophilized powder in a solvent to produce a working solution. Procedure.
- Bacteriostatic water
- Sterile water containing 0.9% benzyl alcohol as a preservative, allowing multiple entries into one vial. Compared with sterile water and WFI.
- Net peptide content
- The peptide fraction of total powder mass, the remainder being counter-ions, water and salts. Explained here.
- Counter-ion
- The ion paired with charged residues after purification, usually acetate (60 g/mol) or trifluoroacetate (114 g/mol).
- TFA
- Trifluoroacetic acid. Standard HPLC mobile-phase additive and a common counter-ion in the isolated salt.
- Free base
- The peptide without its counter-ion. Molecular weights on a COA may be quoted for the free base or the salt; they differ.
- Hygroscopic
- Readily absorbing moisture from air. Lyophilized peptides are hygroscopic, which is why vials are equilibrated to room temperature before opening.
Peptide chemistry
- Amino acid residue
- One amino acid unit within a peptide chain.
- Peptide bond
- The amide linkage joining residues. Absorbs UV around 214 nm, which is why HPLC detection is often set there.
- N-terminus / C-terminus
- The free amino end and free carboxyl end of a chain. Sequences are written N-terminus first.
- Pentadecapeptide
- A peptide of 15 residues. Similarly: tripeptide (3), tetrapeptide (4), octapeptide (8).
- Analog
- A compound structurally modified from a parent sequence — substituted, truncated or extended.
- Fragment
- A defined subsequence of a larger parent peptide or protein, e.g. "(1-29)" denotes residues 1 to 29.
- PEGylated
- Covalently attached polyethylene glycol, which increases molecular size and typically slows clearance in study systems.
- Acetylation / amidation
- Terminal modifications that block the N-terminal amine or C-terminal carboxyl, commonly used to increase stability.
- Deletion sequence
- A synthesis by-product missing one residue. The most common impurity in longer synthetic peptides; appears as a shoulder near the main HPLC peak.
- Deamidation
- Conversion of asparagine or glutamine side chains to aspartate or glutamate — a principal degradation route in solution.
- Aggregation
- Association of peptide chains into larger assemblies, often visible as haze or precipitate.
- Chelation
- Coordination of a metal ion by multiple donor atoms of a molecule, as in the copper complex of the GHK tripeptide. GHK-Cu.
- Freeze-thaw cycle
- One round of freezing and thawing a solution. Repeated cycles promote aggregation and loss of intact peptide; aliquoting avoids them.
Storage
- 2-8 °C
- Standard refrigeration range, used for reconstituted solutions in short-term use.
- −20 °C
- Standard freezer range for long-term storage of lyophilized powder.
- −80 °C
- Ultra-low storage, used for long-term storage of aliquoted solutions.
- Protect from light
- Instruction to store in amber vials or in the dark; several residues, notably tryptophan, are photosensitive.
- RUO (research use only)
- Labelling indicating material is supplied for laboratory research, not for human or veterinary use and not for diagnostic or therapeutic application.
Full compound documentation is published per product in the HolyPeps catalog.
All products are intended for laboratory and research use only. They are not medicines, are not for human or veterinary use, and are not for diagnostic or therapeutic application.