Research peptide glossary

A working glossary of the terms that appear on research peptide specifications, certificates of analysis and supplier listings, written for researchers who buy and handle these compounds rather than synthesise them. Each entry links to the note that covers it in depth. All Alphex products are for laboratory and in-vitro research only.

A to C

• Acetate salt. A peptide isolated with acetate counter-ions on its basic sites. Lighter than TFA and generally preferred for cell work. See acetate versus TFA.
• Aib. Alpha-aminoisobutyric acid, a non-natural residue used to block protease cleavage and bias helical structure. See unnatural residues.
• Aggregation. Self-association of peptide molecules out of solution; visible as haze. Common in lipidated peptides. See lipidated peptides.
• Amino acid analysis (AAA). Hydrolysis and quantification of constituent amino acids; gives composition and net peptide content. See AAA versus HPLC.
• Area percent. The purity calculation: main peak area divided by total peak area. See how purity is calculated.
• Bacteriostatic water. Sterile water with 0.9% benzyl alcohol, for multi-use stocks. See the guide.
• Batch (lot). One synthesis, purification and vialling run, tested as a unit. See batch numbering.
• CAS number. Unique substance identifier. See CAS numbers.
• Certificate of Analysis (COA). The batch's test report. See how to read one.
• Chromatogram. The HPLC trace: signal against time. See how to read one.
• Counter-ion. The ion paired with a peptide's charged sites; part of the vial's mass.

D to L

• D-amino acid. Mirror-image stereoisomer; confers protease resistance, invisible to mass spectrometry. See unnatural residues.
• Deamidation. Asn or Gln converting to acid forms, +0.98 Da. See deamidation and oxidation.
• Deletion sequence. A synthesis impurity missing one residue. See common impurities.
• Endotoxin. Bacterial lipopolysaccharide; measured by LAL, not on standard research peptide COAs. See endotoxin testing.
• ESI-MS. Electrospray ionisation mass spectrometry, the identity test. See ESI-MS explained.
• Fmoc. The temporary amine protecting group used in standard solid-phase synthesis. See SPPS explained.
• Gross weight. Total solid in the vial, including counter-ion and water; what the label states. See net versus gross.
• HPLC / UHPLC. The separation technique behind purity figures. See HPLC versus UHPLC.
• Karl Fischer. Titration for water content. See water content.
• Lipidation. A fatty acid attached to a side chain, changing solubility and adsorption. See lipidated peptides.
• Lyophilised. Freeze-dried. See what lyophilised means.

M to Z

• Monoisotopic mass. Mass using the most abundant isotope of each element; compare like with like against average mass. See molecular weight.
• Net peptide content. Proportion of the solid that is peptide. See net versus gross.
• Oxidation. +16 Da per oxygen on susceptible residues. See deamidation and oxidation.
• Reference standard. Characterised material run alongside a batch to anchor identity and retention. See reference standards.
• Research use only (RUO). The legal basis of sale. See RUO explained.
• Retention time. When a component elutes; identity within a method, not absolutely.
• Scrambled control. Same residues, random order; the key specificity control. See controls and design.
• SPPS. Solid-phase peptide synthesis. See SPPS explained.
• TFA. Trifluoroacetic acid; cleavage reagent, mobile-phase additive and default counter-ion. See acetate versus TFA.
• Truncation. A chain that stopped growing early. See common impurities.
• 220 nm. The peptide-bond detection wavelength used for purity. See 220 versus 280 nm.

Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They are not authorised for human or veterinary use.

Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.

Published 27 April 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.

Alphex Research Team

Alphex Limited, UK research peptide supplier

The Alphex research team writes and maintains these notes for UK laboratories buying research peptides. Every batch Alphex lists is verified by reverse-phase HPLC with a batch-matched Certificate of Analysis. Content covers laboratory and in-vitro research only.