Research peptide glossary

The vocabulary that appears on peptide labels and certificates of analysis, defined plainly. Several of these terms are routinely used in ways that obscure rather than explain — purity and net peptide content in particular are not the same measurement, and the difference is where most confusion in this market lives.

On the vial

What the label is telling you.

Lyophilizedalso: freeze-dried: Dried by freezing the material and then dropping the pressure so the ice sublimates straight to vapour, skipping the liquid phase. It leaves a porous cake or a scatter of flakes that is stable at room temperature far longer than the same peptide in solution. In a 10 mg vial the solid is often barely visible — a film on the glass rather than an obvious powder. Reconstitution guide →
Batchalso: lot: One production run of one compound, identified by its own number. It is the unit that analysis attaches to: a certificate describes a specific batch, not a product line. Two vials of the same compound from different batches are different material and can have different purity.
Excipient: An inactive substance included alongside the peptide, usually mannitol, added as a bulking agent so the freeze-dried cake has physical structure. It is part of the total solid in the vial but not part of the peptide mass.
Desiccant: The sachet of drying agent shipped with lyophilized material. Peptides are hygroscopic — they pull moisture from the air — and absorbed water both degrades the material and makes the stated mass misleading.

On the certificate

The analytical vocabulary, and where it is quietly ambiguous.

Certificate of analysisalso: COA: The document reporting what a laboratory measured for a specific batch. A useful one names the lab, the batch, the date, the method, and reports both identity and purity. A number with no method behind it is an assertion rather than a measurement. How to read one →
HPLCalso: high-performance liquid chromatography: The separation technique used to measure purity. The sample is pushed through a column that separates its components by how strongly each interacts with the packing material; a detector records what comes off and when. Components leaving at different times appear as separate peaks.
HPLC purity: The area of the target peak divided by the total area of all peaks, as a percentage. It answers one question: of the material the detector saw, what fraction was the compound of interest? It does not tell you how much peptide is in the vial — that is a different measurement. What the percentage means →
Chromatogram: The plot the purity figure is derived from: detector response against time. It shows whether the main peak is clean or sitting on the shoulder of something co-eluting with it. A certificate quoting a number without showing the trace is asking to be taken on faith.
Retention time: How long a component takes to travel through the column and reach the detector. Characteristic of a compound under a given method, which is why the method has to be stated for the figure to mean anything.
Mass spectrometryalso: MS: Measures the mass-to-charge ratio of the molecules in a sample, confirming identity — whether the substance is the peptide named on the label. Purity and identity are separate questions: HPLC says how much of the sample is one substance, MS says which substance it is.
Net peptide content: The fraction of total solid that is actually peptide, excluding counterion and residual water. Determined by amino acid analysis or nitrogen determination. Rarely reported, because quoting it makes a product look worse beside a competitor quoting HPLC purity alone — which is exactly why reporting it says something. Why purity figures differ →
Counterionalso: TFA salt, acetate salt: The ion paired with the peptide when it is isolated as a salt — usually trifluoroacetate left from purification, or acetate after an exchange step. It is real mass in the vial, so a batch can be 99.9% pure and still contain appreciably less than the stated mass of peptide.
Deletion sequence: A synthesis failure where one residue does not couple and the chain continues without it, leaving a peptide one residue short. Chemically very close to the target, which is what makes it hard to separate and why longer peptides carry more of it.
Truncated sequence: A chain that stopped growing partway through synthesis and was capped. Like a deletion sequence, it is an impurity that closely resembles the intended molecule.

Preparation and storage

Reagent handling terms.

Reconstitution: Returning lyophilized material to solution by adding a diluent. The technique matters: the diluent is directed down the vial wall rather than onto the cake, and the vial is swirled rather than shaken, because shear and the air-liquid interface generated by shaking denature a fraction of the material. Full guide →
Bacteriostatic water: Sterile water containing 0.9% benzyl alcohol as a preservative. The preservative suppresses microbial growth introduced by repeated stopper punctures, which is what allows a vial to be entered more than once. In stock in Vancouver →
Sterile water for injection: Water with no preservative. Appropriate for single-use preparation and where benzyl alcohol would interfere with an assay. Once entered, a vial made up with it has no protection against contamination.
mg/mL: Concentration: milligrams of peptide per millilitre of solution. Calculated as vial contents divided by diluent volume — 10 mg in 2 mL gives 5 mg/mL. Not a dose; a property of the solution.
Aliquot: A measured portion divided off from a larger volume. Aliquoting a reconstituted solution into single-use portions avoids repeatedly entering one vial and limits freeze-thaw damage.
Freeze-thaw cycle: One round of freezing and returning to liquid. Each cycle costs material through aggregation and denaturation, which is why reconstituted solutions are generally refrigerated rather than frozen and re-frozen. Storage guide →

Regulatory and structural

Terms that carry legal or biochemical weight.

Research use onlyalso: RUO: A designation marking a substance supplied for laboratory investigation rather than diagnosis or treatment. It reflects what a reagent is — chemically characterised, not clinically assessed. It does not convert an unapproved substance into an approved one. What RUO means →
DINalso: Drug Identification Number: The number Health Canada assigns to an authorised drug product, printed on its label. No research peptide sold as an RUO reagent carries one, which is the practical dividing line between a reagent and a medicine in Canada.
Peptide: A chain of amino acids joined by peptide bonds. The distinction from a protein is one of length and convention rather than chemistry — chains up to roughly fifty residues are generally called peptides.
Sequence: The order of amino acids in the chain, written as three-letter or one-letter codes from the N-terminus. It defines the molecule: two peptides with the same composition but different order are different compounds.
Solid-phase peptide synthesisalso: SPPS: The standard manufacturing route. The chain is built one residue at a time on a resin support, each residue coupled, washed and deprotected before the next. Every step is efficient but imperfect, so longer chains accumulate more impurity.
Analogue: A compound deliberately modified from a reference molecule — substituted residues, added groups, altered termini — usually to change stability or receptor selectivity relative to the original.
Agonist: A molecule that binds a receptor and activates it. A dual or triple agonist is engineered to act at two or three receptor types; the difficulty is balancing the activities against one another rather than maximising any one.
Half-life: The time for half of a quantity to be eliminated. In peptide design, resistance to enzymatic degradation and albumin binding are the usual routes to extending it.

Where these terms are used

All products referenced are supplied as laboratory reagents for research use only. Not for human or veterinary use. 19+.