Peptide research glossary

Peptide basics

Amino acid

A small organic molecule containing an amine group and a carboxylic acid group. Amino acids are the building blocks of peptides and proteins.

Peptide bond

The amide bond that links one amino acid to the next in a chain. See What are peptides?

Peptide

A short chain of amino acids joined by peptide bonds, typically fewer than about 50 residues.

Sequence

The order of amino acids in a peptide chain, usually written from the N-terminus to the C-terminus. The sequence defines the molecule.

Molecular formula

The number of atoms of each element in one molecule, for example C₆₂H₉₈N₁₆O₂₂.

Molecular weight

The mass of one molecule, usually given in daltons (Da) or g/mol. Mass spectrometry compares measured mass with this expected value.

CAS number

A unique identifier assigned by the Chemical Abstracts Service to a specific chemical substance.

Research blend

A single vial containing more than one peptide, with a label amount for each component. See What is KLOW peptide? and What is GLOW peptide?

Testing and reports

Batch (lot) number

An identifier linking a vial to a specific production run and its analytical documentation. Look a batch up in our batch report lookup.

Certificate of analysis (COA)

A report of specified tests performed on a batch, such as purity and identity. See How to read a peptide COA.

HPLC

High-performance liquid chromatography. Separates a sample into its components so they can be measured; often used to report purity.

Mass spectrometry (MS)

Measures the mass-to-charge ratio of ions. Used to check that a material's mass matches the expected molecule. See HPLC vs mass spectrometry.

LC–MS

Liquid chromatography coupled to mass spectrometry: components are separated and then their masses measured.

Purity (HPLC area %)

The share of the total detected peak area belonging to the main peak. It is not the same as peptide content or identity. See What does 99% purity mean?

Identity test

A test confirming the material is the intended molecule, commonly by mass spectrometry.

Net peptide content

The proportion of a lyophilised solid's weight that is peptide, as opposed to water, counterions and other components.

Reference report

A laboratory report for a related sample rather than the batch or strength being sold, such as a 10mg report shown for a 5mg product. It does not verify the contents of the vial sold.

Distributor copy

A copy of a laboratory report in which the original client and manufacturer details are replaced with the distributor’s details. The results, batch identifiers and dates are unchanged.

Impurities and stability

Counterion

An ion paired with a charged peptide in the solid, such as trifluoroacetate (TFA) or acetate. See Peptide counterions.

Endotoxin

Lipopolysaccharide from the outer membrane of Gram-negative bacteria. Some cell-based assays are sensitive to endotoxin contamination.

Deamidation

Conversion of asparagine or glutamine side chains, which changes mass by about +1 Da. See Deamidation.

Oxidation

A chemical change, most often at methionine, typically seen as a +16 Da mass shift. See Peptide oxidation.

Aggregation

Peptide molecules associating into larger assemblies, which can affect measurement. See Peptide aggregation.

Deletion or truncation sequence

A related impurity missing one or more residues from the intended sequence. See Sequence impurities.

Hygroscopic

Readily absorbing moisture from the air. Many lyophilised peptides are hygroscopic, which is why vials are kept sealed and dry.

Freeze–thaw cycle

One round of freezing and thawing. Repeated cycles can affect the stability of some materials.

Supply and handling

Lyophilisation

Freeze-drying: removing water from a frozen material under vacuum to leave a dry solid. See Lyophilised peptides.

Bacteriostatic water

Sterile water containing 0.9% benzyl alcohol, a preservative that inhibits bacterial growth. Used as a laboratory diluent.

In vitro

Research carried out outside a living organism, for example in cells, tissues or test tubes. Thistle BioLabs supplies materials for in-vitro research only.

Research use only (RUO)

Supplied for laboratory research and analysis, not for human or veterinary use, diagnosis or treatment. See Research use only.

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