Reference

Glossary of peptide quality-document terms

56 terms, defined the way they appear on certificates, chromatograms, laboratory reports and supplier paperwork. Each entry says what the term proves and what it does not.

A

Acetate salt: The counter-ion form in which many synthetic peptides are supplied after purification. The label or COA may state “acetate” or “TFA”; the salt form changes the gross weight needed to deliver a given amount of peptide, so a figure in milligrams should say whether it refers to the peptide itself or to the salt. See: Purity levels and how they are tested, Lyophilized vs pre-mixed vials.
Adduct: An extra ion attached to a molecule in a mass spectrum, commonly sodium (+22 Da) or potassium (+38 Da). Adduct peaks are expected and are not impurities; a report that explains them is more readable than one that does not. See: HPLC purity vs MS identity.
Amino acid analysisAAA: A method that hydrolyzes a peptide and measures its constituent amino acids. It is one of the ways to measure net peptide content and to confirm composition; it does not confirm sequence order. See: Purity levels and how they are tested.
Appearance: The visual description line on a certificate (for example “white lyophilized powder”). It is a specification, not a test of identity or purity, but a mismatch between the stated appearance and what is in the vial is an early warning worth noting. See: Reading and verifying a COA.
Area-percent purity: The most common purity figure on a peptide COA: the main peak’s area divided by the total area of all peaks in the chromatogram, at a stated wavelength. It assumes every component absorbs similarly and ignores anything that does not elute or absorb, so it is a relative figure, not a mass content. See: HPLC purity vs MS identity, Purity levels and how they are tested.
Average mass: The molecular mass calculated using the natural isotopic abundance of each element. Larger peptides are usually reported by average mass; small ones by monoisotopic mass. A report should say which it used, or the comparison with the expected value will be off by about one dalton per thousand. See: HPLC purity vs MS identity.

B

Blind test: A laboratory test ordered without telling the laboratory which specific product or vendor the sample came from, or a panel designed to identify which of several related compounds is present. The Janoshik report in the registry lists a “common GLP-1 peptide blind test” panel, meaning the laboratory checked which of several listed peptides the sample matched. See: Third-party testing and reading a Janoshik report.

C

Canonical URL: The single authoritative web address of a record. A QR code on a COA that resolves to the manufacturer’s own canonical record URL is a stronger link than one that resolves to a PDF hosted anywhere, because the domain itself is part of the evidence. See: Checking a supplier’s legitimacy.
CAS Registry NumberCAS: A unique identifier assigned to a chemical substance by the Chemical Abstracts Service. A CAS number on a COA lets you look up the expected molecular formula and weight independently; it does not by itself tell you anything about the sample. See: Reading and verifying a COA.
Certificate of AnalysisCOA: A document issued by a manufacturer or laboratory listing the tests performed on a specific lot, the specifications, and the results. A COA is only as good as the identification it carries (product, lot, date, method) and the independence of whoever produced the results. See: Reading and verifying a COA.
Certificate of ConformanceCoC: A statement that a lot meets specification, without the measured results. It is weaker than a COA because there is nothing to re-check; a CoC offered in place of a COA is best read as a prompt to ask for the COA. See: Reading and verifying a COA.
Chain of custody: The documented path a sample takes from the vial to the laboratory: who selected it, how it was sealed, who shipped it, who received it. Independent testing is only as independent as its chain of custody; a sample the vendor chose and sent is not the same as a sample you chose from a received parcel. See: Third-party testing and reading a Janoshik report.
Charge state: In electrospray mass spectrometry a peptide usually carries several protons, so it appears at mass-to-charge values of (M + n)/n rather than at its molecular weight. A report may show several such peaks; software combines them (deconvolution) into one molecular weight. See: HPLC purity vs MS identity.
Chromatogram: The plot produced by an HPLC run: detector signal against time. Each peak is a component eluting from the column. The chromatogram, not the summary number, is what tells you whether the purity figure is believable. See: HPLC purity vs MS identity.
Clone site: A website that copies another company’s pages, photographs, lot codes or documents and presents them under a different brand or domain. Clone sites borrow the original’s evidence; checks such as domain age, image provenance and whether a lot code resolves on the original manufacturer’s domain expose them. See: Checking a supplier’s legitimacy.
Counter-ion: The small ion that balances the charge of a peptide salt, most commonly trifluoroacetate (TFA) left over from purification or acetate after exchange. Counter-ions add to the gross weight and are part of the reason a vial’s stated milligrams can differ from its net peptide content. See: Purity levels and how they are tested.

D

Deconvolution: The software step that converts a series of multiply charged peaks in an electrospray mass spectrum into a single molecular-weight value. A deconvoluted mass without the raw spectrum is harder to audit than one shown with it. See: HPLC purity vs MS identity.
Deletion sequence: An impurity in which one or more amino acids are missing from the intended sequence because a coupling step failed during synthesis. Deletion sequences are close in size and behavior to the target peptide, which is why they can hide under or beside the main HPLC peak. See: Purity levels and how they are tested.
Diastereomer impurity: A peptide with the correct sequence but one amino acid in the wrong stereochemical form (D instead of L), formed by racemization during synthesis. Its mass is identical to the target, so mass spectrometry cannot see it; only chromatography with sufficient resolution can. See: HPLC purity vs MS identity.

E

Electrospray ionization mass spectrometryESI-MS: The mass-spectrometry technique most often used for peptide identity. It produces multiply charged ions from a solution and reports mass-to-charge ratios from which the molecular weight is calculated. It confirms that a molecule of the expected mass is present; it does not by itself quantify purity. See: HPLC purity vs MS identity.

G

GMP claim: A supplier’s statement that it operates under good manufacturing practice. On this site GMP appears only as something to verify: who issued the certificate, for which site and scope, whether the issuing body is a regulator or a private firm, and whether the certificate can be found in the issuer’s own database. See: Verifying GMP claims.
Gradient elution: An HPLC run in which the proportion of organic solvent in the mobile phase increases over time, so that components of increasing hydrophobicity elute in turn. The gradient conditions should appear on the method line of a COA; a steep, short gradient can merge peaks that a slower one would separate. See: HPLC purity vs MS identity.

H

High-performance liquid chromatographyHPLC: The separation technique behind most peptide purity figures. Reversed-phase HPLC with UV detection separates a sample into peaks by hydrophobicity; the main peak’s share of total area is reported as purity. The method conditions determine what the figure can and cannot see. See: HPLC purity vs MS identity, Purity levels and how they are tested.

I

Identity test: A test that confirms the material is what the label says, as opposed to how pure it is. For peptides this is usually a molecular-weight match by mass spectrometry, sometimes supported by sequence or amino acid analysis. Identity and purity are separate questions that need separate evidence. See: HPLC purity vs MS identity.
Impurity profile: The set of components other than the target peptide, with their sizes and, where known, their identities. A COA that reports only a single purity number tells you how much of the sample is the main peak; an impurity profile tells you what the rest is. See: Purity levels and how they are tested.
ISO/IEC 17025: The international standard for the competence of testing and calibration laboratories. Accreditation to it is granted by national accreditation bodies for a defined scope of tests; it can be checked in the accreditation body’s directory, not only on the laboratory’s certificate. See: Third-party testing and reading a Janoshik report.

L

Lot number: The identifier a manufacturer assigns to one production batch. It should appear identically on the vial label, the COA and any public record. A lot number’s format (for example Pepti’s PEP + date + product code) is part of what makes it checkable. See: Reading and verifying a COA, Checking a supplier’s legitimacy.
Lyophilized: Freeze-dried. A lyophilized peptide is supplied as a dry cake or powder from which water was removed under vacuum, which generally improves storage stability compared with a solution. The term describes the physical form, not the purity or the content. See: Lyophilized vs pre-mixed vials.

M

Manufacturer: The party that synthesized and purified the peptide and assigned the lot number. Only the manufacturer can produce lot-level raw data on request; stockists and resellers can only forward what they were given. See: Manufacturer, stockist or reseller.
Mass accuracy: How close a measured mass is to the true mass, usually expressed in parts per million (ppm) or daltons. A report that states the expected and observed mass side by side, with the difference, is easier to judge than one that prints only “conforms”. See: HPLC purity vs MS identity.
Method validation: The documented demonstration that an analytical method is suitable for its purpose, covering parameters such as specificity, linearity, accuracy, precision and range. ICH Q2(R2) is the reference text. A purity figure from an unvalidated method is an observation, not a result you can rely on. See: Purity levels and how they are tested.
Molecular weight: The mass of one molecule of the peptide, calculated from its formula and measured by mass spectrometry. The COA should show the expected value, the observed value and whether both are monoisotopic or average; an observed value alone cannot be checked. See: HPLC purity vs MS identity.
Monoisotopic mass: The mass calculated using the most abundant isotope of each element. It is the value a high-resolution mass spectrometer reports for small peptides and differs slightly from the average mass. Mixing the two conventions produces an apparent mismatch of about one dalton per thousand. See: HPLC purity vs MS identity.

N

Net peptide contentNPC: The proportion of a vial’s gross weight that is actually peptide, after subtracting water and counter-ions. Typical values are well below 100% even for highly pure material, which is why “purity” and “content” must not be read as the same number. See: Purity levels and how they are tested.

P

Peak purity: An assessment, usually by photodiode-array detection, of whether a single chromatographic peak hides more than one component. A high area-percent figure with no peak-purity check leaves open the possibility of co-eluting impurities. See: HPLC purity vs MS identity.
PEP lot code: The lot-numbering convention Pepti uses on its public records: PEP, a six-digit manufacture date (YYMMDD), a hyphen, then a short product-and-strength suffix, for example PEP260712-RT10. The format matters because it can be checked: a PEP code is meaningful only if it resolves to a record on peptioem.com, not on any other domain. See: Checking a supplier’s legitimacy.
Private label: Goods made by one company and sold under another’s brand. A private-label vial’s documents originate with the manufacturer; the brand owner can relabel the product but cannot generate new lot-level data. See: Manufacturer, stockist or reseller.
Public COA library: A manufacturer’s openly browsable collection of lot records, each tied to a lot number and ideally to the vial label by a QR code. It is more checkable than certificates sent one at a time, because anyone can open the same record and compare. See: Reading and verifying a COA.
Purity: On peptide documents, usually shorthand for HPLC area-percent purity: how much of the detected material is the main peak. It is not identity, not content and not a statement about things the method cannot see. The guides on this site read purity figures as answers to the question “pure by which method, at which wavelength, on which day?” See: Purity levels and how they are tested.

Q

QR verification: A code on a label or certificate that, when scanned, opens a record. Its value depends entirely on where it goes: a code that resolves to the manufacturer’s own domain and to the exact lot record is evidence; a code that opens an image or a third-party page is decoration. See: Checking a supplier’s legitimacy.

R

RDAP: Registration Data Access Protocol, the successor to WHOIS for looking up who registered a domain and when. Registration date is the single fastest check against a clone site: a domain registered weeks ago cannot have manufactured the lots it displays months earlier. See: Checking a supplier’s legitimacy.
Reference standard: A well-characterized material against which a sample is compared. Pharmacopoeial reference standards exist for some peptides; where none exists, a laboratory may use a characterized in-house standard and should say so. Whether a standard was used changes what a purity or content figure means. See: Purity levels and how they are tested.
Related substances: Impurities structurally related to the target peptide: deletion sequences, oxidised or deamidated forms, diastereomers, incompletely deprotected species. Reported as individual and total percentages, they are the informative part of a purity result. See: Purity levels and how they are tested.
Reseller: A party that buys finished product from a manufacturer or stockist and sells it on, sometimes under its own label. A reseller’s documents are copies; due diligence therefore focuses on whether those copies trace back to an identifiable manufacturer and lot. See: Manufacturer, stockist or reseller.
Resolution: How well two adjacent chromatographic peaks are separated. Low resolution merges impurities into the main peak and inflates area-percent purity. A method’s resolution for the closest known impurity is more informative than its headline purity figure. See: HPLC purity vs MS identity.
Retention time: The time at which a component elutes from an HPLC column under the stated conditions. Matching retention time against a standard supports identity; retention time alone, without the standard, does not. See: HPLC purity vs MS identity.
Retest date: The date after which a lot should be re-analyzed before use rather than relied on from the original certificate. Many peptide COAs state one; it is a statement about documentation, not a promise about the material’s condition after shipping and storage. See: Reading and verifying a COA.

S

Sample-specific: Describing evidence that applies only to the exact sample tested. One independent report on one vial says nothing about other lots, other strengths or the vendor in general; the registry on this site labels every entry sample-specific for that reason. See: Third-party testing and reading a Janoshik report.
Specification: The acceptance criteria a lot must meet, such as “purity ≥ 98.0% by HPLC” or “molecular weight conforms”. A COA lists specification and result side by side; a result without a specification cannot be judged, and a specification without a result has not been tested. See: Reading and verifying a COA.
Stockist: A party that holds inventory bought from manufacturers and ships from its own stock. A stockist may hold several manufacturers’ lots of the same compound, so the question to ask is which manufacturer and which lot a given shipment comes from. See: Manufacturer, stockist or reseller.
System suitability: Tests run before a chromatographic analysis to show the instrument and column are performing adequately on that day (for example resolution between two known peaks, repeatability of replicate injections of a standard). Their presence on a report is a sign the laboratory follows a documented method. See: Purity levels and how they are tested.

T

Third-party testing: Analysis by a laboratory that is independent of both buyer and seller. Its weight depends on who chose and shipped the sample, whether the laboratory is accredited for the test, and whether the report can be verified on the laboratory’s own website. See: Third-party testing and reading a Janoshik report.

U

UV detection at 214 nm: The wavelength at which the peptide bond absorbs, so it is the usual detector setting for peptide purity. Because every peptide bond absorbs, impurities that are themselves peptides are seen; non-peptide impurities such as salts and water are not. See: HPLC purity vs MS identity.

V

Verification key: A code printed on a laboratory report that lets anyone retrieve the same report from the laboratory’s website. A report without such a key, or whose key does not resolve, cannot be independently confirmed and should be read as a claim. See: Third-party testing and reading a Janoshik report.

W

Water content: The proportion of a lyophilized material that is residual water, measured by Karl Fischer titration or loss on drying. It is part of the difference between gross weight and net peptide content and is rarely reported on research-peptide COAs; its absence is worth noticing. See: Purity levels and how they are tested.
Wayback Machine: The Internet Archive’s store of past snapshots of web pages. It shows when a site first appeared and what it used to say, which makes it a quick check against a supplier that claims a history its domain does not have. See: Checking a supplier’s legitimacy.