What research peptides are, and what "high purity" means on a label

A peptide is a chain of amino acids joined by amide bonds. The convention most chemists use is that anything up to roughly fifty residues is a peptide and anything longer is a protein, though the line is a matter of usage rather than a rule. Nearly everything in this catalog sits well under that mark: Epitalon is four residues, KPV is three, and BPC-157 is fifteen. A few listed items are not peptides at all. NAD+ is a dinucleotide coenzyme, AICAR a nucleoside analogue, MK-677 a small molecule built on a spiroindane scaffold. They sit in a peptide family because that is where people look for them, not because of what they are.

Research reagent, not medicine

"Research peptide" describes how a material is supplied, not what it is chemically. A reagent is sold for laboratory work: it carries a specification, a batch identifier and a test report, and it carries no approval from the FDA, the EMA or any other authority for use in people or animals. Everything on this site is supplied on that basis. Ordering requires an attestation that the material stays in the laboratory, and some destinations are not served at all. The compliance page sets out the details.

That distinction matters for a practical reason as well as a legal one. A medicine is manufactured against a pharmacopoeial monograph, with controls on sterility, endotoxin, residual solvents and much else. A research reagent is manufactured against the specification printed on its certificate, and that specification is usually much narrower: purity by one method, identity by another, sometimes water content. Reading the report tells you what was measured. It says nothing about what was not.

What the purity number is measuring

Most of this catalog is specified at ≥98% purity by HPLC. Reversed-phase high-performance liquid chromatography separates the components of a sample by how strongly they stick to a hydrophobic column, and a UV detector at the far end records what comes off and when. The number reported is an area percentage: the peak belonging to the named peptide divided by the total area of all peaks the detector saw.

Two things follow from that definition and both are easy to miss. Area percent is relative: it compares the main peak to whatever else absorbs UV at the detection wavelength, not to the total mass in the vial. Water, counter-ions and residual salts do not absorb and do not appear. And a purity figure on its own identifies nothing. A 99% pure sample of the wrong peptide still reports 99%.

That is why identity is a separate test. Mass spectrometry ionises the sample and measures the mass-to-charge ratio of what it finds, and the observed mass is compared against the mass calculated from the sequence. Gonadorelin's calculated mass is 1182.3 g/mol; a report showing 1182.3 Da confirms that the molecule in the vial has the composition the label claims. Purity says how much of it there is. Identity says what it is. Neither is useful without the other.

Salts, counter-ions and why the weights differ

Synthetic peptides carrying basic residues are usually isolated as salts, most often acetate or trifluoroacetate. The catalog notes this where it applies; BPC-157 and TB-500 are both supplied as acetates. The molecular weight in the specification table refers to the free peptide unless the entry says otherwise, so the mass in a vial includes counter-ions and residual water that the stated molecular weight does not account for. Peptide content assays exist to quantify that gap, and where a manufacturer reports one it appears on the certificate.

Reading a listing here

Every product page carries the same fields: name, family, catalog identifier, CAS number where one exists, sequence where the manufacturer publishes it, molecular formula, molecular weight, purity specification, form and storage. Where a field is absent it is because the manufacturer does not publish it. The page says so rather than filling the gap with an estimate. Published batch reports live in the report library, which also has a lookup by lot number.

The rest of what people usually want to know about a compound belongs to the literature, not to a storefront. This site describes what is in the vial and what the test report measured, and stops there.