Reference
Glossary
Plain definitions for the vocabulary used across this site — on certificates, on product pages, in the library and in the handling guides. Every term here appears somewhere on the site, and every entry links to the page that uses it.
23 terms
Aliquot
A single-use portion divided out of a larger stock. Splitting a reconstituted vial into aliquots shortly after reconstitution is what lets you take one out of the freezer at a time instead of thawing the whole stock repeatedly.
Amino-acid sequence
Also called Primary sequence, one-letter code
The order of amino acids along the peptide chain, written as one letter per residue. It is the compound's identity: two vials with the same sequence hold the same molecule. Every entry in the library publishes its sequence, and the library search reads sequences as well as names.
CAS number
A registry number assigned by the Chemical Abstracts Service that identifies one substance unambiguously, independent of whatever name a supplier prints on the label. We publish it where the compound has one and omit the row where it does not, rather than estimating.
Certificate of analysis
Also called COA
The laboratory's own report for one specific production lot: what was tested, by what method, and what the result was. A certificate belongs to a lot, not to a product line — a second lot of the same compound gets its own certificate and its own numbers.
Chromatogram
A plot of detector response against time. Each peak is a compound leaving the column, and the peak's position on the time axis is its retention time. It is the raw picture a purity figure is calculated from.
Chromatographic purity
The share of the total peak area that belongs to the target compound, measured by HPLC for one lot. It says how much of what the detector saw was the intended molecule. It does not by itself confirm identity, and it is not the same figure as net peptide content.
Cold chain
Keeping material within its intended temperature range for the whole journey from the laboratory to the bench. A lot is only worth what its certificate says if it arrives in the state it was tested in.
Counter-ion
An ion left over from synthesis and purification that is packaged along with the peptide, most often trifluoroacetate (TFA) or acetate. It is part of the gross mass in the vial but is not peptide, which is why gross mass and net peptide content differ.
Dalton
Also called Da
The unit molecular mass is quoted in. One dalton is roughly the mass of a hydrogen atom. A peptide's mass reflects the whole molecule, including any terminal modification, so it can be higher than the bare sequence alone would suggest.
Freeze-thaw cycle
One round of freezing a solution and thawing it again. Repeated cycles can drive aggregation and oxidation, which is the reason for splitting a reconstituted stock into single-use aliquots.
Gross vial mass
Everything inside the container weighed together — the peptide plus counter-ions, residual solvent and bound water. It is the number on the label, and it is larger than the mass of peptide alone.
HPLC
Also called High-performance liquid chromatography
The separation technique used to test these lots. A sample is pushed through a column so its components come off at different times, and a detector records what arrives. Our certificates report HPLC with UV/VIS detection.
Lot
Also called Batch
One production run of one compound. Lot is the unit that testing attaches to: two lots of the same compound are tested separately and can return different numbers, so a certificate is only meaningful next to the lot number it was issued for.
Lyophilized
Also called Freeze-dried
Dried under vacuum from the frozen state, leaving a solid cake with virtually no water in it. Peptides ship this way because the reactions that degrade them mostly need water, and a dry powder survives transit far better than a solution.
Molecular weight
The mass of one molecule of the compound, quoted in daltons or g/mol. Together with the sequence it is the main identifier used to confirm that a vial holds what the label claims.
Net peptide content
The mass of the peptide itself, with counter-ions, residual solvent and water excluded. This is the figure to use when preparing a stock solution at a known concentration; using gross mass instead makes the stock weaker than intended.
Reconstitution
Dissolving a lyophilized powder back into liquid. The volume of solvent you add sets the concentration of everything you draw afterwards, which is the whole of the arithmetic the calculator does.
Reconstitution water
Also called Bacteriostatic water
Sterile water carrying a low concentration of a bacteriostatic agent, most commonly 0.9% benzyl alcohol. The additive suppresses bacterial growth, which is what allows a vial to be entered more than once over a period rather than used immediately and discarded.
Reference standard
A well-characterised sample of a known compound, run alongside a test sample so the two can be compared. Identity is confirmed by the test material matching the standard, rather than by asserting that the label is correct.
Residue
One amino acid in a chain. It is called a residue rather than an amino acid because forming the peptide bond removes a molecule of water, so what remains in the chain is slightly lighter than the free amino acid was.
Retention time
How long a compound takes to travel through the column and reach the detector. Under fixed conditions it is reproducible, which makes it a first check on identity — though on its own it is a clue rather than proof.
Sterile water
Water rendered free of viable microorganisms, typically by filtration or autoclaving, with no preservative added. Suitable where a preservative is unwanted, but a vial reconstituted with it is intended for immediate use rather than repeated entry.
U-100 unit
A graduation on an insulin syringe, where 100 units correspond to 1 mL. It measures volume, not mass — how much compound a given number of units contains depends entirely on the concentration you reconstituted to.
Where these terms are used
These definitions describe laboratory vocabulary and bench practice. Nothing here describes an application, benefit, dose, route or outcome for any compound. Materials sold by PepXtide are for laboratory research use only, are not for human or animal consumption, and have not been evaluated by the FDA.