What this glossary is for
A peptide Certificate of Analysis is a dense document. It names a molecule, states a batch, and reports a short column of numbers produced by instruments most readers never see. This glossary defines, in plain language, the documentation and analytics terms that appear on that certificate and across these research notes, so that a stated identity can be read and checked rather than taken on trust. Each entry gives a factual definition and a short note on why the term matters for verification. The emphasis throughout is on how a reference material is identified and documented, not on what any compound does. Every specimen in the catalogue is characterised at a university laboratory, the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core, and the resulting certificates are published in the COA library. The terms below are the vocabulary of those documents. For laboratory research use only.
Documentation and traceability
Certificate of Analysis (COA)
A Certificate of Analysis is the document a testing laboratory issues for one specific batch of material. It records the analytical methods used, the identity finding, a figure for how much of the detected material is the named peptide (reported as a % area value), the batch or lot number, and the date, instrument and laboratory. Why it matters for verification: the certificate is what ties a label to a measurement on one real production run, so the identity printed on a vial can be checked against evidence. Reading each field in order is covered in how to read a peptide Certificate of Analysis.
Lot or batch number
A lot or batch number is the code assigned to the material made in a single production run; the same code appears on the vial and on the certificate that documents that run. Why it matters for verification: it is the one link between a physical specimen and the exact document that describes it. Without a matching lot number, a certificate belongs to some other run and cannot stand in for the material in hand. How each run is captured and filed is described in how every batch is documented.
Net peptide content
Net peptide content is the mass of the peptide itself within a dry specimen, as distinct from the total mass of solid in the vial. The total solid also includes counter-ions, bound water and residual salts left from synthesis and purification, so it is usually larger than the peptide alone. Net peptide content is established by analysis, for example amino-acid analysis or quantitative chromatography against a reference standard, rather than read from the fill weight. Why it matters for verification: two vials can hold the same total solid yet contain different amounts of actual peptide, so this figure describes the substance of interest rather than the weight of the powder.
Chemical identity
CAS Registry Number
A CAS Registry Number is a unique numeric identifier assigned by the Chemical Abstracts Service to one defined chemical substance; for example, BPC-157 is commonly cited under 137525-51-0. The number carries no chemical meaning on its own, it simply points to one entry in a central registry. Why it matters for verification: peptide names are often informal, abbreviated, or reused for more than one molecule, so a registry number pins a specimen to a single record that can be cross-checked against public databases. Worked examples of registry identifiers across related compounds appear in the identity comparison of tirzepatide, semaglutide and retatrutide.
Molecular formula and molecular weight
The molecular formula lists how many atoms of each element make up one molecule, such as C62H98N16O22 for BPC-157. The molecular weight is the mass of that molecule, found by summing the masses of those atoms, and is given in daltons (Da) or grams per mole (g/mol); for BPC-157 it is approximately 1419.5 g/mol. A figure quoted as the average molecular weight uses average atomic masses, while a monoisotopic mass uses the single most-abundant isotope of each element and is the value a high-resolution instrument reports. Why it matters for verification: the molecular weight is the theoretical target a mass measurement is matched against; the identity check largely reduces to asking whether the measured mass equals the calculated molecular weight. A fuller single-compound example is the BPC-157 research profile.
Identity versus purity
Identity and purity are two separate questions a certificate answers. Identity asks whether the molecule present is the one named on the label, and is answered by matching a measured mass, and often a retention time, to the expected values. Purity asks what proportion of the detected material is that molecule, and is answered by the % area figure. Why it matters for verification: the two can disagree. A specimen can be the intended molecule yet carry other species alongside it (right identity, lower % area), and a specimen can show one clean peak that is nonetheless the wrong molecule (high % area, wrong identity). A single number cannot settle both questions, which is why identity and quantity are reported separately.
Separation and chromatography
HPLC (high-performance liquid chromatography)
HPLC is a separation technique. A dissolved sample is pushed under pressure through a column packed with fine particles, and because the sample’s components interact with those particles to different degrees, they travel through at different speeds and emerge separately. In peptide work the common form is reversed-phase HPLC, which sorts molecules largely by how water-repelling they are. Why it matters for verification: separating a sample into its parts is what makes it possible to count how many distinct components are present and to measure the relative size of each, which is the basis of the % area figure. HPLC is set beside mass spectrometry in HPLC versus mass spectrometry.
Retention time
Retention time is the interval between loading a sample onto the column and the moment a given component emerges, or elutes, as a peak. Measured under fixed column and solvent conditions, a component elutes at a characteristic and repeatable time. Why it matters for verification: because the time is reproducible when conditions are held constant, retention time acts as a fingerprint that, alongside mass, helps tell one peak from another and flags a peak that does not belong.
Percent area (% area)
Percent area is the area under one chromatographic peak expressed as a percentage of the combined area of all peaks detected in the run. It is read from the chromatogram, the trace of detector signal over time, where each resolved component forms a peak and the area under a peak scales with how much of that component is present. Why it matters for verification: % area is the standard, measurement-based way a certificate states how much of the detected material is the main component, which is why these documents report purity as a % area value rather than as an adjective.
Mass measurement
LC-MS (liquid chromatography and mass spectrometry)
LC-MS couples an HPLC separation directly to a mass spectrometer, so each component is measured by its mass as it leaves the column. The chromatography sorts the sample in time; the mass spectrometer then records the mass of whatever is eluting at each moment. Why it matters for verification: separation alone shows that a peak is present but not what it is. Adding a mass detector attaches a measured mass to each peak, turning “something eluted here” into “this mass eluted here”, which is the step that supports an identity statement.
HRMS (high-resolution mass spectrometry)
HRMS is mass spectrometry carried out on an instrument that resolves mass finely enough to report it to several decimal places. Where a low-resolution reading might record a mass as a whole number, a high-resolution reading distinguishes values that differ only in the third or fourth decimal. Why it matters for verification: a precise measured mass can be compared with the theoretical mass from a molecular formula closely enough to separate the intended molecule from a different species of almost the same mass, a distinction a coarse measurement would miss.
Mass accuracy
Mass accuracy is how close a measured mass sits to the theoretical mass calculated from a molecule’s formula. It is usually expressed in parts per million (ppm): the gap between measured and theoretical mass, divided by the theoretical mass. A smaller ppm figure means a closer match. Why it matters for verification: mass accuracy puts a number on the strength of an identity match, so a confirmation rests on a stated figure rather than on a visual impression that two numbers look alike.
Physical form
Lyophilised (freeze-dried) powder
A lyophilised material has been frozen and then had its water drawn off under vacuum, leaving a dry solid. The same process is written either lyophilised or lyophilized, and the everyday name for it is freeze-drying. Peptides are commonly supplied as a lyophilised white to off-white powder. Why it matters for verification: the physical state is part of a specimen’s documented appearance, and it is the starting point for storage and handling: a dry solid is generally kept cold, dry and shielded from light, and is dissolved in an appropriate laboratory solvent such as sterile water only when a solution is needed for analytical work.
How the terms fit together on a certificate
Read in sequence, these terms describe one chain of evidence. A production run is given a lot number. A sample from it is separated by HPLC, which produces peaks at characteristic retention times and a % area value for each. The separation is coupled to a mass spectrometer (LC-MS), and a high-resolution reading gives a measured mass that is compared, with a stated mass accuracy, against the molecular weight calculated from the compound’s formula and cross-referenced to its CAS number. Together those figures answer the two questions of identity and purity, and the whole record is published as a Certificate of Analysis for that batch. The documents these terms come from are collected in the COA library and explained in the research notes at Learn; the laboratory that produces them for this catalogue is described on the quality and testing page. Individual compounds are worked through in profiles such as GHK-Cu, Tesamorelin and the GLP-1 research peptides overview, and the full catalogue is on the shop page.
For laboratory research use only. Not for human or veterinary use.
Frequently asked questions
What is a Certificate of Analysis for a research peptide?
A Certificate of Analysis is the document a testing laboratory issues for one specific batch of material. It records the analytical methods used, confirmation of the molecule's identity, a % area value for how much of the detected material is the named peptide, the batch or lot number, and the date and instrument. It is what connects the identity printed on a vial to a measurement on a real production run. For this catalogue, certificates are produced at the USC Alfred E. Mann Multi-Omics Mass Spectrometry Core and published in the COA library.
What is the difference between identity and purity on a COA?
Identity is the question of whether the molecule present is the one named on the label, answered by matching a measured mass, and often a retention time, to the expected values. Purity is the question of what proportion of the detected material is that molecule, answered by the % area figure. The two are reported separately because they can disagree: a specimen can be the right molecule accompanied by other species, or a single clean peak that is the wrong molecule.
Why is a peptide tested by both HPLC and mass spectrometry?
The two techniques answer different questions. HPLC separates a sample into its components and measures the relative size of each as a % area value, but on its own it does not identify what each component is. Mass spectrometry weighs each separated component and matches that mass to the value calculated from the compound's formula. Used together, as LC-MS, they show both how much of the detected material is the main component and whether that component is the intended molecule.
What does "% area" mean on a peptide certificate?
Percent area is the area under one chromatographic peak expressed as a percentage of the combined area of every peak detected in the run. Because the area under a peak scales with how much of that component is present, % area is the measurement-based way a certificate states how much of the detected material is the main component. It is the reason these documents express purity as a % area value rather than as a descriptive word.
What is net peptide content, and how is it different from the vial's total weight?
Net peptide content is the mass of the peptide itself in a dry specimen, separate from the total mass of solid in the vial. The total solid also includes counter-ions, bound water and residual salts from synthesis and purification, so it is normally heavier than the peptide alone. Net peptide content is found by analysis rather than read from the fill weight, which is why two vials of equal total weight can hold different amounts of actual peptide.