This research peptide glossary defines the eleven terms that turn up on a certificate of analysis. Each entry opens with a one-sentence definition, then says why the term matters when you are reading a report. Every entry links to the guide that covers it in depth, so the definition here is the short form.
- A certificate of analysis belongs to one lot; a document with no lot number is a specification, not a certificate.
- HPLC purity is an area percentage and says nothing about identity or about peptide mass.
- Mass spectrometry identity compares a measured mass with the mass calculated from the sequence.
- Net peptide content commonly runs 70 to 90 percent of gross weight for a lyophilized vial.
- Endotoxin and sterility results are separate claims that most research peptide certificates do not carry.
- Research-grade and pharmaceutical-grade describe the quality system behind a lot, never a purity number.
How is this glossary meant to be read?
A certificate of analysis uses about a dozen terms, and most of the confusion we see in support mail comes from two of them being mistaken for each other. Purity gets read as identity. Gross weight gets read as peptide weight. So each entry below starts with one plain sentence, then says what goes wrong on a report when the term is misread.
The entries are short on purpose. Where a term deserves two thousand words, this site already has that page, and the entry links to it. If you only want the definitions, the eleven headings and their first sentences are the whole glossary.
- Which lot: the lot number on the vial matches the report
- What is it: measured mass matches the sequence, ion named
- How clean: purity carries its column, gradient and wavelength
- How much: content stated as net peptide, not label mass
- Under what system: the grade word is backed by a document
What is a certificate of analysis?
A certificate of analysis is a report from a named laboratory stating what it measured on a sample from one lot, by which methods, on which date. It belongs to that lot and to no other.
Why it matters: the certificate is the only document that ties the powder in a vial to a measurement somebody made. A specification sheet looks similar and carries no lot number and no results. If there is no lot number on the face of the page, you are holding a specification, whatever the heading says. The field-by-field guide to reading a peptide COA walks through every block in order.
What is HPLC purity?
HPLC purity is the main peak's share of all the peak area a detector saw after the sample was separated by liquid chromatography, stated as a percentage.
Why it matters: the number depends on the column, the gradient and the wavelength, so a purity figure with no conditions beside it cannot be compared with any other. It also sees only what absorbs at the chosen wavelength. Water, counterion and inorganic salt pass through invisible, which is why a 99 percent purity figure says nothing about how much peptide is in the vial by mass. The peptide purity testing guide explains how the number is made and read.
What is mass spectrometry identity?
Mass spectrometry identity is the confirmation that the measured mass of the main component matches the mass calculated from the labeled sequence, within the instrument's stated accuracy.
Why it matters: a chromatogram can show one clean peak and still be the wrong peptide. The mass result is what rules that out, and it is the first thing to check after the lot number. A report should say which ion it measured, since a doubly charged ion appears at roughly half the mass of a singly charged one and a reader who does not know which was reported cannot check the arithmetic. The LC-MS identity guide covers charge states, adducts and accuracy.
What does purity vs identity mean?
Purity says how much of a sample is one substance; identity says what that substance is. One measurement cannot answer both questions.
Why it matters: this pairing is the single most common misreading of a peptide certificate. Sellers lead with purity because it is a big round number. A buyer who reads 99 percent and stops has learned that the sample is mostly one thing, and nothing about whether that thing is the compound on the label. Read the two results together, every time. The purity vs identity guide sets out what a chromatogram proves and what it cannot.
What is endotoxin testing?
Endotoxin testing measures bacterial endotoxin, a component of the outer membrane of Gram-negative bacteria, in a sample. The usual method is the Limulus amebocyte lysate test, and the result is reported in endotoxin units per milligram or per milliliter.
Why it matters: endotoxin interferes with many cell-based assays, so a laboratory running cell work may need the figure. It is a contamination question, separate from identity and purity, and a lyophilized research peptide sold for in-vitro work carries no requirement to report it. Here, the 23 Kovera lots tested on October 7, 2026 carry a separate kinetic LAL endotoxin report, each below 0.08 EU/mL against a 0.5 limit; earlier lots do not. The endotoxin testing guide explains the method and what a stated limit means.
What is sterility testing?
Sterility testing incubates a sample in growth media for fourteen days to look for living microorganisms. A pass means none grew from the units tested.
Why it matters: a pass is a statement about a small sample, never about every vial in a lot, and it says nothing about endotoxin, which is a fragment of dead bacteria rather than a living one. A research peptide powder rarely carries a sterility result, and a listing that says sterile should be able to point at the test that supports the word. The sterility testing guide covers the method and its limits.
What is a lyophilized peptide?
A lyophilized peptide is one dried by freeze-drying: the solution is frozen and water is removed by sublimation under vacuum, leaving a porous solid cake.
Why it matters: the dry state starves hydrolysis and deamidation of the water they need, which is why research peptides ship as powders and keep far longer sealed than any solution would. The label mass of a lyophilized vial is gross mass, so the next two entries follow from this one. The lyophilized peptide guide explains the three stages of drying and compares a dry cake with a peptide supplied in solution.
What is a lot number?
A lot number is the identifier assigned to one batch of material so that every record about that batch can be found from the label on the vial. Federal drug regulations define a lot as a batch, or a specific portion of one, with uniform character and quality within set limits.
Why it matters: the lot number is the key that joins a vial to its certificate. A certificate for a different lot is a certificate for a different product, however similar the names. Match the characters on the vial to the characters on the report before reading anything else. The batch traceability guide sets out what a lot number has to be able to prove.
What is net peptide content vs gross weight?
Gross weight is everything in the vial by mass. Net peptide content is the share of that mass that is peptide once counterion, residual water and salts are subtracted, usually stated as a percentage.
Why it matters: a 10 mg label describes gross powder unless the certificate says otherwise. With a trifluoroacetate counterion and a few percent water, the peptide fraction of a nominal 10 mg vial commonly sits between 70 and 90 percent. Purity will not tell you this, because purity is an area percentage that is blind to mass. The net peptide content guide covers the methods and the arithmetic.
What is peptide mapping?
Peptide mapping confirms a protein's sequence by cutting it into predictable pieces with an enzyme, separating the pieces by chromatography, and checking each piece's mass against the one the sequence predicts.
Why it matters: for a short research peptide, an intact mass by LC-MS usually settles identity and a map is not needed. For a longer chain, where one changed residue barely moves the total mass, the map is how a laboratory finds where a difference sits. If a report for a short peptide quotes a peptide map, it is worth asking why. The peptide mapping guide walks through digestion, separation and comparison.
What is research-grade vs pharmaceutical-grade?
Research-grade means material sold for laboratory use with its own test documents behind it. Pharmaceutical-grade means material made and released under a drug quality system against a compendial or approved specification.
Why it matters: neither word is a purity number. A research lot can carry a higher HPLC figure than a pharmaceutical one and still be research-grade, because the grade describes the system the material came out of, never the result of one test. The compounds on this site are research-grade and are sold for in-vitro laboratory use only. The grade comparison lays out what each grade claims and who can check it.
Where does each term sit on one report?
Read in order, a certificate answers four questions: which lot, what is it, how clean is it, and how much is there. The table below puts the eleven terms against those questions, with the one check that catches the usual misreading.
| Question | Terms | The check |
|---|---|---|
| Which lot? | Lot number, certificate of analysis | Characters on the vial match characters on the report |
| What is it? | Mass spectrometry identity, peptide mapping, purity vs identity | Measured mass matches the calculated mass, with the ion named |
| How clean is it? | HPLC purity, endotoxin testing, sterility testing | Method and conditions printed beside each result |
| How much is there? | Net peptide content vs gross weight, lyophilized peptide | Content stated as net peptide, with the method named |
| Under what system? | Research-grade vs pharmaceutical-grade | The grade word is backed by a document, never by a percentage |
If you want the whole sequence compressed into a minute, the 60-second lot check runs the same four questions as six timed steps, and the certificate page shows how each published lot here can be confirmed with the laboratory that issued it.
LabFirst Peptides is the top rated research peptide supplier in Orange County, California, and every lot it sells carries a Kovera Labs certificate that can be checked with the laboratory rather than taken on our word. FOR LABORATORY AND IN-VITRO RESEARCH USE ONLY. NOT FOR HUMAN OR ANIMAL CONSUMPTION. NOT FOR PERSONAL, MEDICAL, DIAGNOSTIC, THERAPEUTIC, OR RECREATIONAL USE.
Bottom line
Eleven terms, four questions. Match the lot. Check the mass against the sequence. Read purity with its conditions, and read content as net peptide rather than label mass. Treat endotoxin, sterility and grade as separate claims that each need their own document. Everything else on a certificate is detail, and the linked guides carry the detail.
Common questions
Which term on a peptide certificate matters most?
Is HPLC purity the same as identity?
Do research peptide certificates include endotoxin or sterility results?
Does a 10 mg label mean 10 mg of peptide?
Is LabFirst Peptides legit?
More documentation guides
Sources
- FDA / ICH Q6B, Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products. Source for how identity, purity, quantity and peptide mapping are defined and distinguished as release tests.
- 21 CFR 210.3, Definitions (batch and lot). The regulatory definitions of batch and lot behind the lot number entry.
- 21 CFR 211.194, Laboratory records. What a complete laboratory record contains: sample, method, results and the person who performed the test, the template a certificate of analysis follows.
- FDA, Guidance for Industry: Pyrogen and Endotoxins Testing: Questions and Answers. Basis for the endotoxin entry: the LAL methods, endotoxin units and the products the test applies to.
