Peptide COA and Registry Glossary: HPLC, LC-MS, CAS and more

The registry and laboratory terms used on GPC product pages, lot records and certificates of analysis, defined in plain language.

CAS Registry Number: A unique numeric identifier that the Chemical Abstracts Service assigns to one chemical substance. It identifies a molecule without relying on a trade or supplier name, which is why every GPC product page states it.
Molecular formula: The number of atoms of each element in one molecule, written as element symbols with counts, for example C₆₂H₉₈N₁₆O₂₂. Two different molecules can share a formula, so it is read together with the CAS number.
Molecular mass: The mass of one mole of the molecule, stated in grams per mole (g/mol) and calculated from its formula. Mass spectrometry results on a certificate are compared against it.
Amino acid sequence: The order of the amino acids in a peptide chain, written from the N-terminus to the C-terminus in one-letter codes, for example GEPPPGKPADDAGLV. A sequence is omitted on GPC pages when the chain carries modifications a plain string cannot show.
Residue: One amino acid unit within a peptide chain. The residue count on a product page is the number of units in the chain.
C-terminal amide: A chain whose final carboxyl group is replaced by an amide group. It changes the formula and mass, so it is stated in the molecular class.
Acetylation: The addition of an acetyl group, usually at the N-terminus of a chain. An acetylated peptide has a different formula and mass from the unmodified chain.
Acylation: The attachment of an acyl group, such as a fatty diacid side chain, to a residue. The attached group is part of the molecule’s identity and mass.
Cyclic peptide: A peptide whose chain is closed into a ring, for example by a lactam bridge between two side chains or a disulfide bond between two cysteines.
Blend: A vial that holds more than one compound. A blend has no single formula or mass; its product page lists each component with its own registry number and amount.
Lyophilised: Freeze-dried: water is removed under vacuum at low temperature, leaving a dry powder or cake in the sealed vial. Also spelled lyophilized. Lyophilized peptides: freeze-drying and the dry powder
Nominal fill: The amount printed on the label, such as 10 mg per vial. It is the declared fill, not a measurement of the vial in your hand. What the milligrams on a label mean
Net content: The measured amount of peptide in the vial a laboratory tested, reported in milligrams. It can differ from the nominal fill printed on the label. Net peptide content, purity and counterions · Measured content against the label, lot by lot
Counterion: An ion of opposite charge paired with each positively charged group of a peptide in its solid salt form: most often trifluoroacetate left by synthesis and purification, or acetate or chloride after an exchange. Counterions add to the weight of the powder without being peptide, so they lower its net peptide content. How synthetic peptides are made
HPLC-UV purity: A purity figure from high-performance liquid chromatography with ultraviolet detection: the area of the main peak as a percentage of all detected peak area. It describes the tested sample, under that method. Why purity is not peptide content
Chromatogram: The graph behind an HPLC result: detector signal against time. Each peak is a component that left the column at its own retention time.
Retention time: The time, in minutes, at which a component leaves the chromatography column and appears as a peak. It depends on the column and method, so it is compared within one report.
LC-MS identity: An identity check by liquid chromatography coupled to mass spectrometry. The measured masses of the separated component are compared with the masses expected for the declared molecule.
m/z and charge states: Mass spectrometry reports mass divided by charge (m/z). A peptide carrying two extra protons appears as [M+2H]2+, at roughly half its mass plus one; several charge states of one molecule usually appear together.
Bacterial endotoxin: Lipopolysaccharide from the outer membrane of Gram-negative bacteria. Laboratories measure it with an LAL assay and report endotoxin units per milligram (EU/mg).
Heavy metals panel: A measurement of trace elements such as lead, arsenic, cadmium and mercury, commonly by ICP-MS, reported against stated limits.
Net charge: The sum of a peptide’s positive and negative charges at a given pH, counted from its free termini and its acidic and basic side chains. A positive net charge marks a basic peptide and a negative one an acidic peptide; the count depends on the pH and on the pKa values used. Net charge, isoelectric point and pH
Isoelectric point (pI): The pH at which a peptide’s positive and negative charges balance, so its net charge is zero. It is often the pH of lowest solubility, which is why a first solvent is chosen with a pH away from it. Net charge, isoelectric point and pH
Co-solvent: A second solvent, such as DMSO, DMF or acetonitrile, added in the smallest volume that dissolves a peptide before the solution is diluted with water or buffer. It is carried into every dilution, so its final percentage has to suit the method; DMSO and DMF are not removed by freeze-drying. Choosing a first solvent
Stock solution: A solution prepared at a higher concentration than a method needs, labelled with its concentration, solvent and date. Small portions of it are diluted into working solutions, so only a little of the first solvent reaches the assay. Preparing a laboratory stock solution
Working solution: A solution diluted from a stock to the concentration an assay, a calibration or an analytical run actually uses. Being dilute, it loses a larger share of its peptide to container walls and is kept for shorter periods than the stock. Concentration and dilution calculator
Molar concentration: The amount of substance per litre of solution, in mol/L, written in the laboratory as mM (millimoles per litre) or µM (micromoles per litre). Converting from mg/mL needs a molecular weight on the same basis as the amount: the free peptide or its salt form. Concentration and dilution calculator
Dilution factor: The ratio of the final volume to the volume of solution transferred into it. A dilution factor of 10, one part of solution in ten parts in total, lowers the concentration tenfold while the amount of peptide transferred stays the same. Some fields write this as 1:10 and others as 1:9, so a record states the factor itself. Concentration and dilution calculator
Aliquot: A measured portion of a solution, in microlitres, held in its own tube so that it can be thawed once for a single assay or analytical run while the rest stays frozen. A stock solution is divided into aliquots in one session to limit freezing and thawing. Storing peptide solutions
Adsorption (surface loss): The binding of peptide to the surfaces a solution touches, such as tube and vial walls, pipette tips, filters and autosampler vials. A surface holds only so much, so the share lost is larger in a dilute solution; low-binding tubes and fewer transfers lower it. Storing peptide solutions
Freeze–thaw: One freezing and thawing of a solution. As ice forms it concentrates the peptide and any salts and can shift the pH, and oxidation of cysteine, methionine and tryptophan is reported to speed up during freeze–thaw cycles, so laboratories divide a stock into aliquots and thaw each one once. Storing peptide solutions
Certificate of analysis (COA): A laboratory report on one sample from one production batch, at the time of testing. It names the laboratory, the method, the date and the results. Getting a vial analyzed in Canada
Lot and lot code: A lot is one production batch. The GPC lot code printed beside the QR code on each vial links that vial to its lot record and published batch results. Look up a lot
Research use only (RUO): A statement that the material is supplied solely for lawful laboratory research, under the conditions of the Research Use Policy.