In plain English
This page explains the words that come up most often in research papers and on lab paperwork, such as a Certificate of Analysis (a test report for one batch). Each term has a short definition. Where a term needs more space, the entry links to a full guide. The definitions describe how scientists and laboratories use these words. They are not instructions for using any compound.
A
Acetate
A common counter-ion in synthetic peptide salts, derived from acetic acid. Trifluoroacetate is often exchanged for acetate because it can interfere with some analyses and biological studies [7].
Acetylation (N-terminal)
The addition of an acetyl group to a peptide’s N-terminal amino group. It removes the positive charge at that end and changes the molecule’s mass by +42 Da.
Aggregation
The association of peptide molecules into dimers, larger oligomers or insoluble particles. It can be physical (non-covalent) or chemical (for example, disulfide-linked) [5].
Aliquot
A measured portion of a solution, taken so that the stock is not repeatedly opened, thawed or sampled. Peptide solutions are usually stored as single-use aliquots.
Amidation (C-terminal)
The replacement of a peptide’s C-terminal carboxylic acid with an amide group. It removes the negative charge at that end and changes the mass by about −1 Da.
Amino acid
The building block of peptides and proteins. Twenty standard amino acids are encoded genetically, each with a different side chain.
Amino acid analysis (AAA)
A method that hydrolyses a peptide into its amino acids and measures them. It is used to determine peptide content accurately but does not show sequence order [8].
ARTG
The Australian Register of Therapeutic Goods, the TGA’s register of therapeutic goods that can be lawfully supplied in Australia. It can be searched online [14]. Research materials are not entered on it.
Aseptic technique
A set of laboratory practices, such as working in a laminar-flow cabinet and using sterile consumables, that reduce the risk of contaminating sterile materials.
Assay (content)
On a COA, the measured amount of peptide in a sample, usually reported in mg per vial or as a percentage of the labelled amount. It is a different number from purity.
B
Batch (lot)
A quantity of material made in one production run and expected to be uniform. A COA applies to one batch, identified by its batch or lot number.
C
Certificate of Analysis (COA)
A laboratory report on one batch of material, documenting identity, purity, quantity and sometimes contaminants. See How to Read a Peptide COA.
Chromatogram
The trace produced by a chromatography method such as HPLC, showing detector signal against time. Each peak represents one or more compounds.
Cleavage (in synthesis)
The step in solid-phase peptide synthesis that releases the finished peptide from the resin, usually with trifluoroacetic acid, and removes side-chain protecting groups [2].
Counter-ion
An ion of opposite charge that accompanies a charged peptide in its solid salt form, such as trifluoroacetate, acetate or chloride. Counter-ions add mass to the powder but are not peptide [1, 7].
D
Deamidation
A degradation reaction in which asparagine or glutamine loses its side-chain amide, forming aspartic or glutamic acid (or isoaspartate). It adds about 1 Da to the mass [5, 9].
Deletion sequence
An impurity in which one or more amino acids are missing from the intended sequence, usually because of an incomplete coupling or deprotection step during synthesis [1].
Diastereomer
A form of a peptide in which one or more amino acids has the opposite (D instead of L) configuration. Diastereomers have the same mass, so they need chromatographic separation to detect [1].
Disulfide bond
A covalent bond between the sulfur atoms of two cysteine residues. It can link parts of one peptide (forming a ring) or two separate peptides.
E
Endotoxin
Lipopolysaccharide from the outer membrane of Gram-negative bacteria. It can interfere with cell-based experiments even at low levels, and is measured by the LAL test.
Evidence level
A label describing the type of research behind a finding: in vitro, preclinical (animal), early human, clinical trials, or approved medicine. See How to Read Peptide Research.
F
Fmoc
Fluorenylmethyloxycarbonyl, the temporary protecting group used on amino acids in the most common form of solid-phase peptide synthesis [2].
Freeze–thaw
The process of freezing and then thawing a solution. Each repetition exposes the peptide to ice–liquid interfaces and concentration changes that can cause degradation [5].
H
HPLC
High-performance liquid chromatography, a method that separates the components of a mixture as they pass through a packed column. It is the standard method for peptide purity [1].
Hydrolysis
The breaking of a bond by reaction with water. In peptides it cleaves peptide bonds, producing shorter fragments [9].
Hygroscopic
Readily absorbing moisture from the air. Many lyophilised peptides are hygroscopic, and moisture speeds solid-state degradation, so vials are kept sealed and warmed before opening [6].
I
Identity testing
Analysis that confirms a material is the intended molecule, usually by comparing its measured mass (by mass spectrometry) with the theoretical mass [3, 4].
In vitro
Research done outside a living organism, for example in cell culture or test tubes.
In vivo
Research done in a living organism, such as an animal model.
Isoaspartate
An abnormal form of aspartic acid in which the peptide backbone runs through the side chain. It forms during deamidation or aspartate isomerisation and has the same mass as aspartate [9].
Isoelectric point (pI)
The pH at which a peptide carries no net charge. Peptides are usually least soluble near their pI.
K
Karl Fischer titration
A method for measuring water content in a sample. On a peptide COA it shows how much of the powder’s mass is water.
L
LAL test
The Limulus amebocyte lysate test, which detects bacterial endotoxin. It does not detect living microbes, which need separate sterility testing.
LC-MS
Liquid chromatography coupled to mass spectrometry. It separates components and measures their masses in one analysis, so it can identify impurity peaks.
Lyophilisation
Freeze-drying: freezing a solution and removing the ice by sublimation under vacuum. It produces a dry powder that is much more stable than the solution [10].
M
Mass spectrometry (MS)
A method that measures the mass-to-charge ratio of ions. For peptides, it confirms molecular mass and therefore identity.
Molar mass (molecular weight)
The mass of one mole of a substance, in g/mol. It is used to convert between mass concentration (mg/mL) and molar concentration (µM).
N
Net peptide content
The percentage of a lyophilised powder’s mass that is actually peptide, with water and counter-ions excluded. It is needed to calculate true peptide concentration [8].
O
Oxidation
A chemical reaction that adds oxygen to, or removes electrons from, a molecule. In peptides it mainly affects methionine, cysteine, histidine, tryptophan and tyrosine [11].
P
Peptide
A chain of amino acids joined by peptide bonds. Peptides are generally shorter than proteins, often under about 50 residues. See What Are Peptides?.
Peptide bond
The amide bond that links the carboxyl group of one amino acid to the amino group of the next.
Preclinical
Research done before any human studies, usually in cell and animal models.
Protecting group
A temporary chemical group that blocks a reactive site on an amino acid during synthesis, so that bonds form only where intended [2].
Purity (HPLC)
The proportion of the peptide material that is the target sequence, usually reported as the main peak’s percentage of total peak area on an HPLC chromatogram [1].
R
Racemisation
Conversion of an amino acid from its natural L-form to a mixture with the D-form. It can occur during synthesis or degradation and produces diastereomeric impurities [1, 9].
Reconstitution
Dissolving a lyophilised material in a solvent to make a solution of known concentration.
Reference standard
A highly characterised sample of known identity and content, used to calibrate analytical methods and assign values to test samples [8].
Residue
A single amino acid within a peptide chain. A 15-residue peptide contains 15 amino acids.
Retention time
The time a compound takes to pass through a chromatography column to the detector. It helps identify peaks, but on its own does not prove identity.
Reversed-phase HPLC (RP-HPLC)
The most common HPLC mode for peptides, which separates molecules by hydrophobicity using a non-polar column and a water–organic solvent gradient.
S
Salt form
The form in which a charged peptide is isolated, together with its counter-ion, for example a trifluoroacetate or acetate salt [7].
Schedule (Poisons Standard)
A category in Australia’s Poisons Standard that sets how a substance may be supplied, for example Schedule 4 (prescription only). Some substances are also listed in Appendix D, clause 5, which means possessing them without authority is illegal [12]. See Are Peptides Legal in Australia?.
Sequence
The order of amino acids in a peptide, written from the N-terminus to the C-terminus using one- or three-letter codes.
Solid-phase peptide synthesis (SPPS)
The standard method for making synthetic peptides, in which the chain is built one amino acid at a time on an insoluble resin. Fmoc-based SPPS is now the method of choice [2]. See How Research Peptides Are Made.
Specificity (analytical)
The ability of an analytical method to measure the intended analyte unequivocally, without interference from other substances present [3].
Stability
The ability of a material to keep its identity, purity and content over time under defined storage conditions [5, 6, 10].
Succinimide
A five-membered ring intermediate formed during deamidation of asparagine and isomerisation of aspartate. It hydrolyses to aspartate or isoaspartate [9].
T
TFA (trifluoroacetic acid)
A strong acid used in peptide cleavage and HPLC purification. Many synthetic peptides are therefore supplied as trifluoroacetate salts [7].
U
UV-Vis spectrophotometry
A method that measures how much ultraviolet or visible light a sample absorbs. Without a separation step it cannot distinguish a peptide from closely related impurities.
V
Validation (analytical method)
Documented evidence that an analytical method is fit for its intended purpose, covering characteristics such as accuracy, precision, specificity and range [3].
W
WADA
The World Anti-Doping Agency, which publishes the Prohibited List of substances banned in sport.
What this means in Australia
Several terms in this glossary have legal meanings in Australia.
- ARTG. A product that is not entered on the Australian Register of Therapeutic Goods is not approved for supply as a medicine in Australia [14].
- Schedule and Appendix D. The current Poisons Standard is the October 2026 instrument (F2026L01327). Schedule 4 means prescription-only, and Appendix D, clause 5 means possessing a listed poison without authority is illegal. Some research peptides, such as BPC-157 and TB-500, are named in both [12].
- “Research use only”. The TGA has stated that a “research use only” disclaimer does not make supply of an unapproved peptide product lawful. It does not change regulatory status, permit importation, or remove advertising or supply obligations [13].
See Are Peptides Legal in Australia? for more detail.
This is general information, not legal advice. Laws change; check the current Poisons Standard and TGA guidance.
Frequently asked questions
What does lyophilised mean?
Lyophilised means freeze-dried: the material was frozen and its ice removed under vacuum, leaving a dry powder that is more stable than a solution [10].
What is the difference between purity and peptide content?
Purity is the share of peptide material that is the correct sequence. Peptide content is the share of the whole powder that is peptide at all, once water and counter-ions are excluded [1, 8].
What is a counter-ion?
A counter-ion is the oppositely charged ion that accompanies a charged peptide in its salt form, such as trifluoroacetate or acetate [7].
What is the difference between HPLC and LC-MS?
HPLC separates components and measures purity. LC-MS adds mass spectrometry, so each separated component can also be identified by its mass.
References
- D’Hondt M, Bracke N, Taevernier L, et al. Related impurities in peptide medicines. J Pharm Biomed Anal. 2014;101:2–30. doi:10.1016/j.jpba.2014.06.012. PMID: 25044089
- Behrendt R, White P, Offer J. Advances in Fmoc solid-phase peptide synthesis. J Pept Sci. 2016;22(1):4–27. doi:10.1002/psc.2836. PMID: 26785684
- International Council for Harmonisation. ICH Q2(R2): Validation of analytical procedures. 2023. database.ich.org. Accessed 11 October 2026.
- International Council for Harmonisation. ICH Q6B: Specifications: test procedures and acceptance criteria for biotechnological/biological products. database.ich.org. Accessed 11 October 2026.
- Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharm Res. 2010;27(4):544–575. doi:10.1007/s11095-009-0045-6. PMID: 20143256
- Lai MC, Topp EM. Solid-state chemical stability of proteins and peptides. J Pharm Sci. 1999;88(5):489–500. doi:10.1021/js980374e. PMID: 10229638
- Roux S, Zékri E, Rousseau B, Paternostre M, Cintrat JC, Fay N. Elimination and exchange of trifluoroacetate counter-ion from cationic peptides: a critical evaluation of different approaches. J Pept Sci. 2008;14(3):354–359. doi:10.1002/psc.951. PMID: 18035848
- Li C, Bhavaraju S, Thibeault MP, et al. Survey of peptide quantification methods and comparison of their reproducibility: a case study using oxytocin. J Pharm Biomed Anal. 2019;166:105–112. doi:10.1016/j.jpba.2018.12.028. PMID: 30640042
- Geiger T, Clarke S. Deamidation, isomerization, and racemization at asparaginyl and aspartyl residues in peptides: succinimide-linked reactions that contribute to protein degradation. J Biol Chem. 1987;262(2):785–794. PMID: 3805008
- Wang W. Lyophilization and development of solid protein pharmaceuticals. Int J Pharm. 2000;203(1–2):1–60. doi:10.1016/s0378-5173(00)00423-3. PMID: 10967427
- Li S, Schöneich C, Borchardt RT. Chemical instability of protein pharmaceuticals: mechanisms of oxidation and strategies for stabilization. Biotechnol Bioeng. 1995;48(5):490–500. doi:10.1002/bit.260480511. PMID: 18623513
- Commonwealth of Australia. Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026 (F2026L01327). legislation.gov.au/F2026L01327/latest/text. Accessed 11 October 2026.
- Therapeutic Goods Administration. Understanding your responsibilities when importing, compounding and supplying unapproved peptide products. Safety advisory, 13 April 2026. tga.gov.au. Accessed 11 October 2026.
- Therapeutic Goods Administration. Australian Register of Therapeutic Goods (ARTG) search. tga.gov.au/resources/artg. Accessed 11 October 2026.
Important information and disclaimer
General information only. This article is published for general educational and informational purposes. It summarises published scientific literature and public regulatory information as at the “last reviewed” date shown above. It is not medical, health, pharmaceutical, veterinary or legal advice, and it must not be relied on as a substitute for advice from a qualified professional about your circumstances.
Not for human or animal use. Nothing in this article recommends, endorses or describes the use of any substance in humans or animals. Findings from cell, animal or early human studies cannot be assumed to apply to people. The compounds discussed have not been evaluated by the Therapeutic Goods Administration (TGA) for safety, quality or efficacy unless the article expressly states otherwise. Any research materials offered by Iconic Peptides are supplied solely for in vitro and laboratory research.
No therapeutic claims. Iconic Peptides makes no claim that any product treats, cures, prevents, alleviates or diagnoses any disease, condition or symptom. References to published studies, clinical trials or medicines approved by regulators are factual descriptions of the scientific and regulatory record. They are not representations about any product we supply.
Regulatory status. Many peptides are scheduled substances under the Poisons Standard. Some are prescription-only (Schedule 4), and some may not be possessed without authority (Appendix D). The TGA has stated that a “research use only” label does not make supply lawful, change a product’s regulatory status, or remove advertising or supply obligations. State and territory laws may also apply. You are responsible for knowing and complying with all laws that apply to you. Regulatory information in this article may change after the review date.
Accuracy and third-party sources. We take care to cite and verify every source, but we do not warrant that this article is complete, current or error-free. Citing a study or organisation does not mean that its authors or that organisation endorse Iconic Peptides.
Limitation of liability. To the maximum extent permitted by law, Iconic Peptides, its owners, employees and contributors exclude all liability for any loss, damage, injury or expense, whether direct, indirect or consequential, arising from use of or reliance on this article or any misuse of any product. Nothing in this disclaimer excludes, restricts or modifies any right or remedy under the Australian Consumer Law that cannot lawfully be excluded.
Age restriction. This website is intended for adults aged 18 and over.
