A peptide paperwork glossary

Thirty-six entries for the terms that appear on peptide certificates, labels and regulatory pages, each defined in one to three sentences from a primary source and linked to the piece that explains it.

By Touchstone PeptidesSeptember 22, 202611 minute read

Certificates of analysis, vial labels and regulators' lists share one vocabulary, and each entry below defines a term from it in one to three sentences, drawn from the standard or agency that defines it. Every entry links to the piece on this site that explains the term in full. Regulatory entries carry a date because they change; the rest is stable chemistry and measurement vocabulary, and none of it is guidance on the use of any product.

Numbers

503A. Section 503A of the Federal Food, Drug, and Cosmetic Act covers compounding by a state-licensed pharmacy or a licensed physician, where, in FDA's words, "the drugs must be compounded based on the receipt of valid patient-specific prescriptions". A 503A compounder is exempt from FDA approval and manufacturing-practice requirements only under the section's conditions. See 503A, 503B and research-use-only.

503B. Section 503B covers outsourcing facilities registered with FDA, which "are subject to CGMP requirements" and "may distribute compounded drugs either pursuant to a patient-specific prescription or in response to an order from a health care provider, such as a hospital, that is not for an identified individual patient". Neither 503A nor 503B has anything to do with a research vial. See 503A, 503B and research-use-only.

A to C

Acetate. The counter-ion left on a peptide when trifluoroacetate has been exchanged for acetic acid's anion. It weighs less than trifluoroacetate per charge and changes the net peptide content of the solid. See TFA salt or acetate salt.

Amino-acid analysis (AAA). A quantitative method in which the peptide is hydrolysed to its constituent amino acids, which are then separated and measured; Bachem describes it as determining amino-acid composition via hydrolysis and HPLC. It is one of the routes to net peptide content. See net peptide content.

Area percent. The basis of an HPLC purity figure: the area of the main peak divided by the total area of all peaks, expressed as a percentage. ICH Q2(R2) lists "area percent with respect to the major analyte" as one basis for reporting impurities. It assumes every peak responds to the detector alike. See why two laboratories get different numbers.

Batch. FDA defines a batch as "a specific quantity of a drug or other material that is intended to have uniform character and quality, within specified limits, and is produced according to a single manufacturing order" in one run of manufacture (21 CFR 210.3). ICH Q7 uses batch and lot interchangeably. See what a lot number is for.

Bulks list (503A). FDA's list of bulk drug substances that may be used in 503A compounding when a substance has no USP or NF monograph and is not a component of an approved drug. Adding a substance requires rulemaking. As of September 21, 2026, none of the research peptides discussed on this site is on it. See Category 1, Category 2 and the 503A bulks list.

CAS Registry Number. A unique identifier for a substance assigned by CAS, a division of the American Chemical Society; CAS describes it as "a unique and unambiguous identifier for a specific substance". Every product page here carries one where CAS has assigned it. See what a peptide is.

Category 1, 2 and 3 (503A interim policy). FDA's holding categories for nominated bulk substances while it evaluates them. Category 1 substances "may be eligible for inclusion on the 503A bulks list" and were nominated with sufficient information; for Category 2, "FDA has identified significant safety risks"; Category 3 nominations lacked sufficient information. As of September 21, 2026, twelve peptides that were in Category 2 from September 29, 2023 sit in a "nominated but withdrawn" section (FDA page dated April 22, 2026) and are in no category. See Category 1, Category 2 and the 503A bulks list.

Certificate of analysis (COA). A document issued for a specific batch that, per ICH Q7, "should list each test performed in accordance with compendial or customer requirements, including the acceptance limits", with the numerical value for each, dated and signed, with the manufacturer's name and address. See how to read a certificate of analysis.

Counter-ion. The oppositely charged ion that balances a peptide's charged residues in the solid; for synthetic peptides it is usually trifluoroacetate and sometimes acetate or chloride. Sikora and colleagues note it may be "directly bonded with basic residues of peptides or adsorbed in lyophilizate". See TFA salt or acetate salt.

D to H

Endotoxin. Lipopolysaccharide from the outer membrane of Gram-negative bacteria, measured in endotoxin units. Its limit for a parenteral product is set by USP <85> as K divided by M, where K is 5.0 EU/kg body weight, so no single "EU/mg" limit exists without an assumption about M. See endotoxin testing and EU/mg.

EU (endotoxin unit). The unit in which endotoxin activity is reported, defined against a reference standard endotoxin. Certificates that state "EU/mg" are reporting activity relative to the mass of solid tested. See endotoxin testing and EU/mg.

HPLC and RP-HPLC. High-performance liquid chromatography separates the components of a dissolved sample by pumping it through a packed column; reversed-phase HPLC uses a non-polar column (typically C18) and a water-to-organic gradient, which suits peptides. With UV detection near 214 to 220 nm it gives the purity figure on a certificate. See reading a chromatogram.

I to L

ICP-MS. Inductively coupled plasma mass spectrometry, the technique used to measure elemental impurities such as lead, cadmium, arsenic and mercury; it is the usual basis for the elemental-impurities test described in USP <232> and <233>. Most research certificates do not include it. See sterility, heavy metals and residual solvents.

Import alert. An FDA instruction that lets its field divisions detain a listed firm's shipments without examination. Import Alert 66-41, "Detention Without Physical Examination of Unapproved New Drugs Promoted In The U.S.", revised May 19, 2026, is the one whose Red List includes firms whose peptide shipments were detained; the alert itself is not peptide-specific. Status as of September 21, 2026. See Import Alert 66-41.

INCI name. The International Nomenclature Cosmetic Ingredient name, the labelling name under which a cosmetic ingredient is declared; the Personal Care Products Council states that ingredients are "identified by a single labeling name regardless of the national origin of the product". Names are developed by the International Nomenclature Committee and published by the Council. A research vial is not sold under an INCI name. See cosmetic-grade versus research-grade peptides.

ISO/IEC 17025. The international standard for the competence of testing and calibration laboratories. A laboratory is "ISO 17025 accredited" only if an accreditation body such as A2LA, ANAB or NVLAP has assessed it against the standard and issued a certificate with a scope; ISO itself accredits no one. See how to verify a peptide lab report.

Karl Fischer. A reagent-based method for measuring water content, reported as a percentage of the solid. FDA's lyophilization inspection guide calls the moisture in vials "an obvious concern with the lyophilized product". The water figure is part of the gross mass and not part of the peptide. See fill weight and label accuracy.

LAL. Limulus amoebocyte lysate, the horseshoe-crab-derived reagent used in the bacterial endotoxins test. FDA states that "For more than 30 years, FDA has accepted the use of a Limulus Amoebocyte Lysate (LAL) test for endotoxins in lieu of the rabbit pyrogens test"; recombinant reagents are the newer alternative. See endotoxin testing and EU/mg.

LC-MS. Liquid chromatography coupled to mass spectrometry: the column separates the sample and the mass spectrometer reports the mass-to-charge ratio of what elutes, most often by electrospray ionisation, which "often produces multiply charged species". It is the usual identity test on a peptide certificate. See mass spectrometry identity.

Lot. FDA defines a lot as "a batch, or a specific identified portion of a batch, having uniform character and quality within specified limits" (21 CFR 210.3). A fill of one label mass can be a lot within a larger batch of bulk peptide. See what a lot number is for.

Lot number. "Any distinctive combination of letters, numbers, or symbols, or any combination of them, from which the complete history of the manufacture, processing, packing, holding, and distribution of a batch or lot" can be determined (21 CFR 210.3). It should be identical on the vial, the packing slip and the certificate. See what a lot number is for.

Lyophilized. Freeze-dried. FDA's inspection guide describes lyophilization as "three separate, unique, and interdependent processes; freezing, primary drying (sublimation), and secondary drying (desorption)". The white cake in a vial is what remains once the water has sublimed. See what lyophilized means.

M to P

MALDI. Matrix-assisted laser desorption/ionisation, a mass-spectrometry ion source suited to "medium and large-sized, polar, heat-sensitive compounds" that typically yields singly charged ions. It is an alternative to electrospray for confirming a peptide's mass. See mass spectrometry identity.

Monoisotopic mass. The "mass calculated from the exact masses of the most abundant isotopes of its constituent elements", the figure a high-resolution mass spectrometer reports for a peptide below a few thousand daltons. The average mass, weighted by isotope abundance, is the molecular weight on a product page; the two differ by up to about a dalton for small peptides. See mass spectrometry identity.

Net peptide content (NPC). Bachem's definition: "the fraction of peptidic material (i.e. the requested peptide and the peptidic impurities) relative to counter-ions and residual water". Net weight equals gross weight multiplied by NPC. It is the number that turns a label mass into a peptide mass. See net peptide content.

PubChem CID. The compound identifier assigned by PubChem, the NIH National Library of Medicine's open chemistry database; a CID record carries the structure, molecular formula, molecular weight and monoisotopic mass. Product pages here cite the CID where one exists. See what a peptide is.

R to S

Reconstitution. In laboratory usage, the dissolution of a lyophilized solid in a solvent to give a solution of known concentration. On a certificate the word describes a sample-preparation step before analysis. This site does not publish reconstitution or use guidance for any product. See vial, spray or strip.

Residual solvents. Organic solvents remaining from synthesis and purification, controlled under ICH Q3C and measured by gas chromatography in the test described in USP <467>. They are rarely reported on a research certificate. See sterility, heavy metals and residual solvents.

Retest date. ICH Q7: "The date when a material should be re-examined to ensure that it is still suitable for use." Q7 adds that for an active ingredient "Common practice is to use a retest date, not an expiration date", and that it "should be based on an evaluation of data derived from stability studies". See six ways a certificate of analysis misleads.

Research use only (RUO). A labelling statement, not a regulatory exemption for peptides. The only "For Research Use Only" provision in FDA's regulations, 21 CFR 809.10(c), applies to in vitro diagnostic products. Under 21 CFR 201.128 intended use is judged by objective intent, shown in claims, advertising and the circumstances of distribution, not by a disclaimer. See what "research use only" actually means and what FDA reads before calling a research product a drug.

Sterility test (USP <71>). The compendial procedure, by membrane filtration or direct inoculation into culture media, applied to articles required to be sterile. It is a lot-release test on a sample; it does not prove a process or a vial is sterile, and a research certificate that lacks it is not claiming sterility. See sterility, heavy metals and residual solvents.

T to U

TFA (trifluoroacetate). The anion of trifluoroacetic acid, used to cleave a synthetic peptide from its resin and as the acid in reversed-phase purification, so that "cationic peptides are obtained as trifluoroacetate salts" (Sikora et al.). It is the usual counter-ion on a research peptide and a substantial part of the non-peptide mass. See TFA salt or acetate salt.

USP <85> Bacterial Endotoxins Test. The compendial chapter describing the gel-clot, photometric and kinetic LAL methods and the K/M basis for setting a limit. FDA's guidance states that "The appropriate way to establish the endotoxins limit is to use the calculation methods provided in the USP or AAMI standards." See endotoxin testing and EU/mg.

WADA Prohibited List. The World Anti-Doping Agency's annual list of substances and methods prohibited in sport, in force from January 1 each year. Its status is separate from FDA status: BPC-157 is named in section S0 (non-approved substances) of the 2026 List, and GHRH analogues, growth hormone secretagogues and thymosin beta-4 derivatives appear under S2. As of September 21, 2026. See WADA S0, S2 and strict liability.

Sources

For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.

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