This glossary collects the terms most often encountered on certificates of analysis, product datasheets, and method papers in peptide research. Definitions are intentionally short; deeper articles in the Learn hub expand on most entries.
A
Acetate counter-ion. The most common salt form of synthetic peptides, present as an artefact of TFA exchange after RP-HPLC purification. Reported on the COA as a percentage of net peptide content.
Aliquot. A measured sub-volume of a stock solution dispensed into a single-use vial to avoid repeated freeze–thaw cycles.
Amino acid. The monomeric building block of peptides. The 20 proteinogenic L-amino acids plus selenocysteine and pyrrolysine are encoded; many non-natural and D-amino acids are used in research peptides.
Anhydride coupling. A historical activation chemistry; modern SPPS uses HBTU/HATU/DIC/Oxyma esters instead.
B
Bacteriostatic water. Sterile water containing 0.9% benzyl alcohol as a preservative; widely used as a reconstitution diluent for research peptides intended for repeated draws over weeks.
BSA. Bovine serum albumin, often used as a carrier protein to coat plasticware and reduce non-specific peptide adsorption.
Boc. tert-Butyloxycarbonyl, an N-terminal protecting group used in older Boc/Bzl SPPS chemistries.
C
CAS number. A unique numerical identifier assigned by the Chemical Abstracts Service; useful for SDS, customs and inventory matching.
COA. Certificate of Analysis. A lot-specific QC record that lists at minimum: peptide identity, sequence, lot, mass, purity by HPLC, mass-spec confirmation, water content, and counter-ion percentage.
Counter-ion. The salt species accompanying the peptide (typically acetate or TFA); affects net peptide mass per vial.
CPP. Cell-penetrating peptide; short cationic or amphipathic sequences (e.g. TAT, penetratin) used to deliver cargo across the plasma membrane.
D
DMSO. Dimethyl sulfoxide, a polar aprotic solvent used to dissolve hydrophobic peptides at minimal volume; cytotoxic above 0.1–1% in cell assays.
DKP. Diketopiperazine, a cyclic by-product of premature deletion or epimerisation during synthesis.
E
ESI-MS. Electrospray-ionisation mass spectrometry; the standard mass-confirmation method on a peptide COA.
Endotoxin. Lipopolysaccharide contamination from gram-negative bacteria; relevant where peptides are used in cell or animal models. Quantified by LAL assay.
F
Fmoc. 9-Fluorenylmethyloxycarbonyl, the dominant N-terminal protecting group in modern SPPS.
FA. Formic acid, an LC-MS-compatible mobile-phase additive.
G
GHRP. Growth-hormone-releasing peptide, a class that includes GHRP-2 and GHRP-6.
GLP-1 agonist. A peptide that activates the glucagon-like peptide-1 receptor; semaglutide and tirzepatide are research-relevant examples.
H
HPLC. High-performance liquid chromatography. Reverse-phase HPLC (C18) is the standard purity assay for synthetic peptides; results are reported as area-percent.
Hygroscopic. Readily absorbing atmospheric moisture; lyophilised peptides should be equilibrated to room temperature before opening to avoid condensation onto the cake.
I
IDP. Intrinsically disordered peptide/protein.
Impurity profile. The list of peaks adjacent to the main peptide on the HPLC trace, including deletion sequences, epimers, and oxidation products.
L
LC-MS. Liquid-chromatography–mass spectrometry; combines purity (LC) with identity (MS) confirmation.
Lyophilisation. Freeze-drying. Removes water under vacuum to leave a stable solid cake.
M
Mass spec (MS). A confirmation method that measures the peptide’s monoisotopic or average mass; the observed value must match the theoretical mass within instrument tolerance.
MOQ. Minimum order quantity; the smallest size or count at which an item is offered.
Monoisotopic mass. The mass calculated using the most abundant isotope of each element; the value reported by high-resolution MS.
N
Net peptide content. Mass of the peptide itself in a vial after subtracting water and counter-ion. Always lower than the gross fill mass.
O
Oxidation. A common degradation mode for cysteine, methionine and tryptophan residues; minimised by argon overlay and reducing agents.
P
Pegylation. Conjugation of polyethylene glycol to a peptide to increase aqueous solubility or modify pharmacokinetics in research models.
Peptide bond. The amide linkage between the carbonyl of one amino acid and the amine of the next.
R
Reconstitution. Dissolving a lyophilised peptide in a chosen diluent (bacteriostatic water, sterile water, dilute acetic acid, or DMSO) prior to use.
Reverse-phase HPLC. The standard separation mode for peptides (non-polar C18 stationary phase, aqueous–acetonitrile gradient with TFA or FA additive).
RUO. Research Use Only — products labelled RUO are not for human, veterinary or diagnostic use.
S
Salt form. See counter-ion.
Sequence. The ordered list of amino-acid residues in single-letter or three-letter code, written N-terminus to C-terminus.
SPPS. Solid-phase peptide synthesis; the dominant industrial method, originated by R. B. Merrifield.
T
TFA. Trifluoroacetic acid; a common HPLC ion-pairing additive that often persists as the peptide counter-ion when not actively exchanged.
Tm. Melting temperature of a structured peptide or duplex.
U
UV detection. Most peptide HPLC traces are recorded at 220 nm (peptide bond) and 280 nm (Trp/Tyr).
V
Vial fill. The total mass deposited in a vial including peptide, counter-ion and residual water; the COA gives the breakdown.
W
Water content. Residual water remaining after lyophilisation; quantified by Karl Fischer titration on the COA.
Z
Zwitterion. A neutral molecule with separate positively and negatively charged groups; many peptides are zwitterionic at physiological pH.