Whether you’re new to peptide research or a seasoned scientist looking for a quick reference, this A-Z glossary covers the essential terminology used in peptide science, reconstitution, quality analysis, and in-vitro laboratory research. Each term is defined in accessible, accurate language with links to our detailed guides and tools where relevant.

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A

Amino Acid

The fundamental building blocks of peptides and proteins. There are 20 standard amino acids encoded by DNA, each with a unique side chain that determines its chemical properties. Amino acids are linked together by peptide bonds to form peptide chains. Each amino acid is represented by both a three-letter code (e.g., Gly for glycine) and a single-letter code (e.g., G).

Analog

A synthetic peptide that has been structurally modified from a naturally occurring sequence to alter its properties — such as improved stability, enhanced receptor binding, or extended half-life. Many research peptides are analogs of endogenous hormones or signaling molecules.

Assay

A laboratory procedure used to measure the presence, amount, or activity of a substance. In peptide research, common assays include receptor binding assays, cell viability assays, and enzyme activity assays. Assay results are only reliable when peptides are properly reconstituted and stored.

B

Bacteriostatic Water (BAC Water)

Sterile water containing 0.9% benzyl alcohol as a preservative. BAC water is the preferred solvent for reconstituting research peptides because the benzyl alcohol inhibits bacterial growth, allowing multi-use access to the vial over approximately 28 days. See our bacteriostatic water vs sterile water comparison for detailed guidance.

Benzyl Alcohol

The antimicrobial preservative present in bacteriostatic water at a concentration of 0.9% (9 mg/mL). It works by disrupting bacterial cell membranes, preventing microbial growth in reconstituted peptide solutions.

Bioavailability

The proportion of a substance that enters circulation or reaches the site of action when introduced to a biological system. In peptide research, bioavailability varies significantly based on the route of administration used in animal research models.

BPC (Body Protection Compound)

A protein isolated from human gastric juice. BPC-157, a 15-amino acid synthetic fragment of this protein, is one of the most widely studied research peptides. See our BPC-157 reconstitution guide for detailed protocols, or learn more about what research peptides are and how they’re used in laboratory settings.

C

Certificate of Analysis (COA)

A document issued by a testing laboratory that details the identity, purity, and quality of a specific batch of peptide. A credible COA includes HPLC purity data, mass spectrometry results, and is ideally performed by an independent third-party lab. COAs are your primary tool for verifying peptide quality. Learn how to read a peptide COA in our detailed guide.

Concentration

The amount of peptide dissolved per unit volume of solution, typically expressed as mg/mL (milligrams per milliliter) or µg/mL (micrograms per milliliter). Concentration is determined by the amount of peptide in the vial and the volume of solvent added during reconstitution. Use our reconstitution calculator to determine your target concentration.

Counterion

A charged ion that accompanies the peptide to maintain electrical neutrality. Research peptides typically come as acetate or trifluoroacetate (TFA) salts. The counterion contributes to the total vial weight but is not part of the active peptide content, which is why net peptide content is always less than the labeled total weight.

Cysteine

An amino acid containing a sulfhydryl (-SH) group that can form disulfide bonds with other cysteine residues. These bonds are important for peptide structure but make cysteine-containing peptides susceptible to oxidation during storage and handling.

D

Dalton (Da)

The standard unit of molecular mass used in biochemistry. One Dalton equals approximately the mass of a single hydrogen atom (1.66 × 10⁻²⁴ grams). Peptide molecular weights are expressed in Daltons or kilodaltons. See also: Kilodalton.

Deamidation

A chemical degradation reaction in which asparagine or glutamine residues lose their amide group, converting to aspartate or glutamate respectively. Deamidation occurs more readily in aqueous solution and at elevated temperatures, which is one reason lyophilized storage is preferred.

Degradation

The breakdown of a peptide’s chemical structure over time, resulting in loss of purity and biological activity. Degradation can occur through hydrolysis, oxidation, deamidation, or aggregation. Proper storage and handling minimize degradation. See our peptide storage guide.

Dosage

The specific amount of peptide used in a research protocol, typically expressed in micrograms (µg) or milligrams (mg). Accurate dosing requires knowing your solution’s concentration and measuring volumes precisely with calibrated syringes. Our peptide dosage calculator simplifies this math.

E

Excipient

An inactive substance added to a peptide formulation for stability, bulking, or pH adjustment. Common peptide excipients include mannitol (a bulking agent that improves the lyophilized cake structure), trehalose (a stabilizing sugar), and buffer salts. Excipients are listed on the COA.

Endotoxin

Lipopolysaccharides released from the cell walls of gram-negative bacteria. Endotoxin contamination in peptide preparations can interfere with cell-based assays by triggering inflammatory responses. High-quality peptide vendors test for endotoxin levels and report results on the COA.

F

Freeze-Dried

See Lyophilization. The terms “freeze-dried” and “lyophilized” are used interchangeably in peptide research. Both refer to the process of removing water from a peptide solution under vacuum at low temperature to produce a stable, dry powder.

FMOC (Fluorenylmethyloxycarbonyl)

A protecting group used in solid-phase peptide synthesis (SPPS). FMOC chemistry is the most common method for synthesizing research peptides. The FMOC group temporarily protects the amino terminus of each amino acid during the stepwise addition process, then is removed before the next amino acid is coupled.

G

GLP-1 (Glucagon-Like Peptide-1)

An incretin hormone consisting of 30-31 amino acids that plays a role in glucose metabolism. GLP-1 receptor agonist analogs — including semaglutide and tirzepatide analogs — are among the most actively studied research peptides. See our semaglutide reconstitution guide and tirzepatide reconstitution guide.

GMP (Good Manufacturing Practice)

A set of quality standards and guidelines for the manufacturing of pharmaceutical and research products. GMP-certified facilities follow strict protocols for cleanliness, documentation, quality control, and traceability. Peptides manufactured under GMP conditions typically command higher prices but offer greater quality assurance.

H

Half-Life

The time required for half of a given quantity of peptide to be eliminated or degraded in a biological system. Half-life is a critical parameter in research protocol design, as it determines dosing frequency in animal studies. Peptide half-lives range from minutes (for many natural peptides) to days (for engineered analogs with modifications like PEGylation or fatty acid conjugation).

HPLC (High-Performance Liquid Chromatography)

The primary analytical method used to determine peptide purity. HPLC separates the target peptide from impurities based on chemical properties (typically hydrophobicity in reverse-phase HPLC), then quantifies each component. Purity is reported as the percentage of the total chromatographic area represented by the target peptide peak. A purity of ≥95% is standard for research-grade peptides. Learn more in our COA reading guide.

Hydrolysis

The chemical breakdown of peptide bonds by water molecules. Hydrolysis is one of the primary degradation pathways for peptides in solution, which is why lyophilized (anhydrous) storage dramatically extends shelf life.

I

In-Vitro

Latin for “in glass.” Refers to experiments conducted outside of a living organism, typically in test tubes, petri dishes, or other laboratory vessels. In-vitro research is the appropriate context for the use of research peptides. Distinct from in-vivo (in a living organism) research.

Insulin Syringe

A syringe calibrated in “units” (where 100 units = 1 mL for U-100 syringes) commonly used for measuring and transferring peptide solutions. Insulin syringes feature fine-gauge needles suitable for precise small-volume measurements. See our insulin syringe units guide for a complete explanation of how to read and use them.

Isoelectric Point (pI)

The pH at which a peptide carries no net electrical charge. At its isoelectric point, a peptide is least soluble in aqueous solution, which is relevant when choosing reconstitution solvents and buffers. Peptides with very acidic or basic pI values may require pH-adjusted solvents for optimal dissolution.

J

Janoshik Analytical

A widely recognized independent analytical testing laboratory that provides third-party Certificate of Analysis (COA) testing for research peptides. Janoshik testing is considered a gold standard for verifying peptide purity and identity. Vendors like Chameleon Peptides publish Janoshik COAs for every batch, providing researchers with independent quality verification. Learn how to interpret COA results.

K

Kilodalton (kDa)

A unit of molecular mass equal to 1,000 Daltons. While most research peptides have molecular weights in the range of hundreds to a few thousand Daltons (0.5-5 kDa), the kilodalton unit is commonly used for larger peptides and small proteins.

L

Lyophilization

The process of freeze-drying a peptide solution to produce a stable, dry powder. Lyophilization involves freezing the solution, then reducing pressure to allow frozen water to sublimate directly from ice to vapor. The resulting lyophilized powder is significantly more stable than the peptide in solution, with shelf lives of years versus weeks. Most research peptides are sold in lyophilized form. See our detailed comparison of lyophilized vs liquid peptides.

Lyophilized Cake

The solid, porous structure that remains in the vial after lyophilization. A well-formed cake appears as a uniform white or off-white plug at the bottom of the vial. The cake structure allows rapid dissolution when reconstitution solvent is added. A collapsed or discolored cake may indicate improper manufacturing or storage.

M

Mannitol

A sugar alcohol commonly used as an excipient (bulking agent) in lyophilized peptide formulations. Mannitol helps form a stable, well-structured lyophilized cake and improves the reconstitution properties of the final product.

Mass Spectrometry (MS)

An analytical technique that measures the mass-to-charge ratio of molecules. In peptide analysis, mass spectrometry confirms the molecular weight of the synthesized peptide matches the expected value, verifying that the correct sequence was produced. Common variants include MALDI-TOF and ESI-MS. Mass spec data is a standard component of peptide COAs.

Molecular Weight (MW)

The sum of the atomic masses of all atoms in a peptide molecule, expressed in Daltons (Da) or grams per mole (g/mol). Molecular weight is a fundamental identifying property of a peptide — if the mass spec result doesn’t match the expected MW, the peptide may be incorrect or impure. Every peptide has a unique theoretical molecular weight calculated from its amino acid sequence.

N

Net Peptide Content

The actual mass of active peptide in a vial, expressed as a percentage of the total weight or as an absolute mass. Total vial weight includes counterions, residual moisture, and excipients. Net peptide content is typically 60-80% of the labeled total weight and is the value that should be used when calculating reconstitution concentrations.

O

Oxidation

A chemical degradation reaction that particularly affects peptides containing methionine, cysteine, and tryptophan residues. Exposure to oxygen, light, or metal ions accelerates oxidation. Oxidized peptides may show reduced biological activity. Proper storage under inert atmosphere (nitrogen or argon) and protection from light minimize oxidation risk.

P

Peptide Bond

The covalent chemical bond formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH₂) of another, with the release of a water molecule. Peptide bonds link amino acids together into peptide chains. They are relatively stable but can be broken by hydrolysis, enzymatic cleavage, or extreme pH conditions.

PEGylation

The attachment of polyethylene glycol (PEG) chains to a peptide molecule. PEGylation increases the peptide’s molecular size, reduces renal clearance, and extends its half-life in biological systems. Many modern peptide analogs use PEGylation or similar modifications to improve pharmacokinetic properties.

Purity

The proportion of the total vial contents that is the intended target peptide, expressed as a percentage. Purity is measured primarily by HPLC and is the most important quality metric for research peptides. Higher purity means fewer impurities that could confound experimental results. Research grade is typically ≥95%; high-purity grade is ≥98%. See our COA reading guide for interpreting purity data.

R

Receptor Binding

The interaction between a peptide ligand and its target receptor protein. Receptor binding assays are a common application for research peptides, measuring how strongly and specifically a peptide interacts with its biological target. Binding affinity is typically expressed as a dissociation constant (Kd).

Reconstitution

The process of dissolving a lyophilized (freeze-dried) peptide powder back into solution by adding a measured volume of solvent, typically bacteriostatic water. Proper reconstitution technique involves adding solvent gently down the side of the vial and swirling (never shaking) to dissolve. Use our reconstitution calculator for precise volume calculations and read our step-by-step reconstitution guide for the complete process.

Research Compound

A chemical substance, including synthetic peptides, manufactured and sold exclusively for in-vitro laboratory research, scientific study, and educational purposes. Research compounds are not intended for human consumption and are not approved medications.

Residual Moisture

The small amount of water remaining in a lyophilized peptide after the freeze-drying process, typically less than 1-3% of the total weight. Excessive residual moisture can accelerate degradation during storage. Residual moisture is sometimes reported on COAs.

Reverse-Phase HPLC (RP-HPLC)

The most common HPLC method used for peptide analysis. In RP-HPLC, the stationary phase is hydrophobic (typically C18-bonded silica) and the mobile phase is a water/organic solvent gradient. Peptides elute in order of increasing hydrophobicity, allowing separation of the target peptide from impurities.

S

Sequence

The specific order of amino acids in a peptide chain, written from the N-terminus (amino end) to the C-terminus (carboxyl end). The sequence defines a peptide’s identity and determines its physical, chemical, and biological properties. Sequences are written using either three-letter or single-letter amino acid codes.

Solid-Phase Peptide Synthesis (SPPS)

The standard method for manufacturing synthetic peptides. In SPPS, amino acids are added one at a time to a growing peptide chain that is anchored to an insoluble resin bead. After the full sequence is assembled, the peptide is cleaved from the resin and purified. SPPS enables efficient, automated production of peptides up to approximately 50 amino acids in length.

Stability

The ability of a peptide to maintain its chemical structure, purity, and biological activity over time under specified conditions. Stability depends on the peptide sequence, storage conditions (temperature, light, moisture), formulation, and whether the peptide is lyophilized or in solution. See our peptide storage guide for stability optimization.

Sterile Water for Injection (SWFI)

Purified water that has been sterilized but contains no preservatives. SWFI is suitable for single-use reconstitution but should not be used for multi-dose vials, as bacterial contamination can occur without the preservative effect of benzyl alcohol. See our bacteriostatic water vs sterile water guide.

Subcutaneous (SC/SubQ)

A route of administration used in animal research models, referring to injection beneath the skin into the subcutaneous tissue layer. Many peptide research protocols in preclinical animal studies utilize subcutaneous administration due to relatively consistent absorption rates.

Sublimation

The phase transition from solid directly to gas, bypassing the liquid phase. Sublimation is the core physical process in lyophilization — frozen water in the peptide solution sublimates under vacuum, leaving the dry peptide behind.

Synthesis

The chemical process of creating a peptide by linking amino acids together in a specific sequence. Modern peptide synthesis primarily uses solid-phase methods (SPPS) with FMOC chemistry, followed by purification via HPLC to achieve the desired purity level.

T

TFA (Trifluoroacetic Acid)

A strong acid commonly used in peptide synthesis and purification. TFA serves as a counterion in many peptide formulations (peptide TFA salt), contributing to the total vial weight but not to the active peptide content. Some protocols require TFA-to-acetate salt exchange for specific applications.

Titer

The concentration of a substance in solution as determined by a specific analytical test. In peptide research, titer is sometimes used to describe the measured concentration of a reconstituted peptide solution.

U

USP (United States Pharmacopeia)

A standards-setting organization that establishes quality specifications for pharmaceutical ingredients, including solvents used in peptide reconstitution. USP-grade bacteriostatic water meets strict purity, sterility, and endotoxin standards. Always use USP-grade solvents for peptide research.

V

Vial

The sealed glass container in which lyophilized peptides are supplied. Research peptide vials are typically 2 mL or 3 mL clear glass vials sealed with a rubber stopper and aluminum crimp cap. The vial is designed to maintain sterility and should be accessed only with a sterile syringe through the rubber stopper after wiping with an alcohol swab.

Void Volume

In HPLC analysis, the volume of mobile phase required to elute an unretained compound through the column. Understanding void volume is relevant when interpreting HPLC chromatograms on peptide COAs, as peaks appearing at or near the void volume represent highly polar impurities.

W

Wetting

The initial contact between reconstitution solvent and lyophilized peptide powder. Proper wetting technique involves directing the solvent stream down the inside wall of the vial rather than directly onto the powder cake, allowing the solvent to gradually saturate the lyophilized material without disrupting its structure.

Using This Glossary

This glossary is designed as a living reference for peptide researchers. For hands-on guidance, explore our tools and detailed articles:

This glossary is intended for educational and informational purposes related to in-vitro laboratory research only. Peptides referenced herein are research compounds and are not intended for human consumption. Definitions are provided for general reference and may not cover all specialized contexts. Always follow your institution’s protocols and applicable regulations when conducting research.