Peptide testing glossary
41 terms you will meet on a certificate of analysis or a research compound record, each defined in a sentence or two, with a link to the guide that explains it at length.
- Accession number
- The testing laboratory's unique reference for one test report. Looking it up on the lab's own website brings up the lab's copy of that report. Verifying a COA at the lab
- Acetate salt
- A peptide isolated with acetate as its counterion. Acetate is one of the two most common counterions on synthetic peptides, alongside trifluoroacetate (TFA). Purity vs net content
- Acetylation
- Adding an acetyl group, written Ac-, usually to the N-terminus (the first residue). It changes the peptide's mass and charge and is part of its stated structure.
- Amidation
- Ending a peptide in an amide (-NH2) instead of a free acid at the C-terminus (the last residue). Written -NH2 at the end of a sequence.
- Amino acid analysis
- A method that breaks a peptide into its amino acids and measures each one. It is one of the ways a lab measures net peptide content. Purity vs net content
- Batch
- A quantity of one compound made in one run and handled as a single unit. Used interchangeably with lot. Lot numbers explained
- CAS number
- A unique identifier the Chemical Abstracts Service assigns to a chemical substance, such as 137525-51-0. One substance, one CAS number, whatever it is called.
- Certificate of Analysis (COA)
- The laboratory document that records the test results for one lot: what was tested, the methods, the purity, the identity result, the net content and the lab that ran it. How to read a COA
- Chromatogram
- The trace an HPLC run produces: detector response plotted against time, with one peak for each component the column separates. Reading the chromatogram
- CLIA
- The Clinical Laboratory Improvement Amendments, the US federal certification program for clinical laboratories that test human specimens. A CLIA number identifies a laboratory site in that program and the certificate type it holds. Why third-party testing matters
- Cold chain
- Shipping that holds a product at a set low temperature the whole way. Sealed lyophilized peptide tolerates room temperature in transit, so our orders ship without ice. Storing sealed powder
- Counterion
- The oppositely charged ion that pairs with a peptide when it is isolated as a salt, such as acetate or trifluoroacetate. It adds to the weight of the powder but is not peptide. Purity vs net content
- D-amino acid
- The mirror-image form of an amino acid. Proteins are built from L-amino acids; a D-residue, written with a D- prefix such as D-Ala, is a deliberate change to a synthetic sequence.
- Desiccant
- A drying agent, such as silica gel, kept near a sealed vial to absorb moisture from the surrounding air. Storing sealed powder
- Endotoxin
- A molecule from the outer membrane of certain bacteria. An endotoxin test measures how much is present in a sample, in endotoxin units (EU).
- Heavy metals
- Metallic elements such as lead, mercury, cadmium and arsenic. A heavy-metals test measures each one in a sample, usually in parts per million.
- HPLC
- High-performance liquid chromatography. It separates a sample's components on a column and measures each as a peak; peptide purity is the target peak's share of the total peak area. How purity is measured
- Hygroscopic
- Taking up water from the air. Many peptide powders are hygroscopic, which is why a vial is kept sealed and dry. Storing sealed powder
- Identity test
- The test that confirms a sample is the compound on the label, usually by mass spectrometry: the measured mass is compared with the expected molecular weight. Reading the chromatogram
- Label claim
- The amount the label states, such as 10 mg. A certificate that reports net content lets you compare the measured amount with the label claim. Purity vs net content
- LC-MS
- Liquid chromatography coupled to mass spectrometry: the sample is separated by chromatography and each component's mass is measured as it comes off the column. How purity is measured
- Lot
- One batch of a compound made and tested together, identified by a lot number such as BPC-10-001. Every vial from a lot shares one certificate. Lot numbers explained
- Lyophilized
- Freeze-dried: the water is removed under vacuum at low temperature, leaving a dry powder or cake that stays stable in storage and in transit. Storing sealed powder
- Mass spectrometry (MS)
- A method that turns molecules into ions and measures their mass-to-charge ratio. Used to confirm a compound's identity against its expected molecular weight. Reading the chromatogram
- Molecular formula
- The count of each kind of atom in one molecule, such as C62H98N16O22. Two different compounds can share a formula; a CAS number tells them apart.
- Molecular weight
- The mass of one molecule, in grams per mole (g/mol) or daltons. It is the value an identity test compares the measured mass against.
- Monoisotopic mass
- A molecule's mass counting only the most common isotope of each element. It is slightly lower than the average molecular weight, so a comparison uses the same kind on both sides. Reading the chromatogram
- m/z
- Mass-to-charge ratio, the horizontal axis of a mass spectrum. An ion carrying two charges appears at about half its mass. Reading the chromatogram
- Net peptide content
- How much of the powder in a vial is peptide, after water and counterions are counted out, reported as a percentage or in milligrams per vial. Purity vs net content
- Peak area
- The area under one peak on a chromatogram, which is proportional to how much of that component the detector saw. Purity is the main peak's area as a share of the total. Reading the chromatogram
- Peptide bond
- The amide bond that joins one amino acid to the next in a peptide chain. It absorbs UV light near 214 nm, which is why HPLC detectors read peptides there.
- PubChem CID
- The compound identifier in PubChem, the public chemistry database run by the US National Library of Medicine. Each of our compound records links its CID where one exists.
- Purity
- The share of the peptide material in a sample that is the target compound, measured by HPLC and reported as a percentage. It is a ratio, not a mass. What 99%+ purity means
- Reference standard
- A sample of known identity and content that a lab measures alongside the test sample, so the result can be expressed as an amount. Purity vs net content
- Residue
- One amino acid unit within a peptide chain. A 15-residue peptide is built from fifteen amino acids joined by peptide bonds.
- Retention time
- How long a component takes to pass through the HPLC column, in minutes. Under one method the same compound comes off at the same time. Reading the chromatogram
- Sequence
- The order of the amino acids in a peptide, written from the N-terminus to the C-terminus in three-letter codes (Gly-His-Lys) or one-letter codes (GHK).
- Solid-phase peptide synthesis (SPPS)
- The usual way research peptides are made: the chain is built one amino acid at a time while anchored to a resin, then cleaved, purified and freeze-dried. How peptides are made
- TFA salt
- A peptide isolated with trifluoroacetate (TFA) as its counterion, common because TFA is used in synthesis and HPLC purification. Purity vs net content
- Third-party testing
- Testing by a laboratory independent of the seller. Its value depends on the lab being named and its reports being checkable on the lab's own site. Why third-party testing matters