Reference
Plain definitions for the terms that appear on a certificate of analysis, and what each one does and does not tell you about a batch.
A laboratory document reporting what was measured on one specific batch.
A certificate of analysis reports the measurements a laboratory made on a named batch of material. It applies only to the batch tested — not to the product line, and not to a later batch of the same compound. A certificate without a lot number on it cannot be matched to anything you hold.
The identifier tying a certificate to a specific batch of material.
A lot number appears on both the vial and the certificate, and is what makes an analytical record verifiable rather than decorative. If the lot on the label does not appear on the certificate you were given, the certificate describes different material.
The quantity stated on the label, as distinct from the quantity measured.
Label claim is what the product says it contains. Measured net weight is what the laboratory found. The two are reported side by side because the difference is the informative part; a certificate showing only one of them is difficult to interpret.
The mass of material the laboratory actually recovered and weighed.
Reported in milligrams against the label claim. Small variances in either direction are normal in lyophilised material. Large ones are the reason to read the number rather than assume it.
High-performance liquid chromatography — separates a mixture into its components.
HPLC pushes a dissolved sample through a column that separates compounds by how strongly they interact with it. Each component emerges at a characteristic time, producing the peaks on a chromatogram. It is the basis of most purity determinations.
The proportion of UV-absorbing material attributable to the main peak.
A detector measures ultraviolet absorbance as compounds leave the HPLC column. Purity is the main peak's area as a percentage of total peak area. The important limitation: it only counts what absorbs at the chosen wavelength. Anything transparent at that wavelength — many salts, some solvents — is invisible to the measurement and does not reduce the figure.
The detection wavelength used on the certificates published here.
Peptide bonds absorb strongly in the low ultraviolet, roughly 205 to 215 nm, so wavelengths in that band detect the peptide backbone itself and are a general-purpose choice for peptide purity. Higher wavelengths such as 280 nm respond mainly to aromatic residues, so a peptide lacking tryptophan, tyrosine or phenylalanine can be badly under-detected there.
Measures molecular mass to confirm identity.
Liquid chromatography separates the sample; the mass spectrometer then measures the mass-to-charge ratio of what emerges. Purity and identity answer different questions — HPLC tells you how much of the material is one thing, mass spectrometry tells you what that thing is. Neither substitutes for the other.
A charged form of a molecule, which is what a mass spectrometer actually detects.
Mass spectrometers measure ions, not neutral molecules, so a sample is ionised first. [M+H] means one proton was added, giving a detected mass about one unit above the true molecular weight. [M+2H] carries two protons across two charges, appearing at roughly half the mass. This is why a detected value never exactly equals the molecular weight, and why a single compound can produce several peaks.
The mass of one molecule, in grams per mole.
A compound's molecular weight is fixed, so it is a useful check on a certificate: a reported mass that does not match the known value for the named compound means the sample, the label, or the certificate is wrong. Related forms differ — a copper-complexed peptide is heavier than the free peptide by the mass of the copper it carries.
A bacterial cell-wall component, quantified in endotoxin units per milligram.
Endotoxins are lipopolysaccharides shed by gram-negative bacteria. They are heat-stable and survive many processes that kill the organism itself, which is why endotoxin is measured separately rather than inferred from sterility.
The test used to quantify endotoxin.
Limulus amebocyte lysate reacts with bacterial endotoxin, and the extent of that reaction is measured to give a value in EU/mg. It is a specific test that is performed or not performed on a given batch — where a certificate carries no LAL result, no endotoxin measurement was made on that batch.
The proportion of a sample that is peptide rather than salts and water.
Distinct from purity. Purity describes the composition of the peptide fraction; peptide content describes how much of the total mass that fraction is. Lyophilised peptides commonly carry counter-ions and residual water, so material can be highly pure and still be a minority of the vial by mass. This matters for calculating molar concentration. The certificates published on this site report purity, identity and — where performed — endotoxin; they do not report peptide content.
Freeze-drying: removing water by sublimation under vacuum.
The sample is frozen and the pressure lowered so ice passes directly to vapour without melting. It produces a stable dry solid without the heat that would degrade a peptide, which is why most research peptides are supplied lyophilised.
Returning lyophilised material to solution.
Dry peptide is dissolved in an appropriate solvent before use. Which solvent is appropriate depends on the compound's solubility, listed per compound in the catalog.
Material supplied for laboratory research and not for any human or animal use.
An RUO designation describes the terms on which material is supplied. It is not a drug approval, not a claim of safety, and not a statement that the compound is suitable for any diagnostic or clinical purpose. Everything on this site is supplied RUO.
A quantity of material produced in one run under the same conditions.
Analytical results apply to the batch tested. Two batches of the same compound are separate material with separate certificates, which is why records here are organised by lot rather than by product.
The plot of detector response over time produced by a chromatographic run.
Peaks correspond to components leaving the column, with position indicating retention time and area indicating relative quantity. It is the underlying evidence a purity percentage is derived from.
How long a component takes to travel through the column.
Characteristic of a compound under a given method, so a shifted retention time can indicate a different compound or a changed method. Comparable only between runs using the same conditions.
Analysis performed by a laboratory independent of the manufacturer.
Independence matters because the party with an interest in the result is not the party producing it. The analytical results published on this site were generated by AxisPharm, LLC, an independent laboratory; the manufacturer did not produce them.
The date to which the supplier expects the material to remain within specification.
Distinct from a pharmaceutical expiry date, which carries a regulatory meaning that does not apply to research material. A best-by date is a storage expectation, not a guarantee, and depends on the material having been stored as directed.
When the batch was produced.
Read alongside the best-by date and the date the certificate was issued. A large gap between manufacture and testing is worth noticing, since analytical results describe the material at the time it was tested.
These definitions describe what the terms mean, not what any particular batch contains. For the measured results on a specific lot, see the COA library. For longer treatments of how the methods work and where they fall short, see the analytical guides.
