Quick answer
An endotoxin tested peptide is one whose lot was checked for bacterial endotoxin (lipopolysaccharide) with an LAL or recombinant Factor C assay, with the value reported on the COA in endotoxin units per milligram (EU/mg). HPLC purity cannot show endotoxin: 1 EU is roughly 0.1 ng, far below what an HPLC trace can see. A complete peptide COA therefore reports three separate checks: HPLC purity, mass-spec identity and endotoxin.
BPC-157 10mg · lot-specific COA included with every order
Table of Contents
- What Are Endotoxin Tested Peptides?
- Key Facts
- What Are Endotoxins in Peptides?
- Why HPLC Purity Doesn’t Show Endotoxin
- Peptide Endotoxin Testing Methods: LAL and rFC
- Peptide Endotoxin Levels: How to Read EU/mg
- How to Read a Peptide COA
- Keeping Endotoxin Out During Lab Prep
- What Published Studies Examined
- Standards and Regulatory Status
- Endotoxin Testing and the CoreVionRX COA
- Frequently Asked Questions
What Are Endotoxin Tested Peptides?
Endotoxin tested peptides are research peptides whose production lot has been checked for bacterial endotoxin, with the method and the measured value written on the certificate of analysis (COA). The check is a separate test from purity and identity.
The standard methods are the Limulus amebocyte lysate (LAL) assay and the newer recombinant Factor C (rFC) assay. Both report endotoxin in endotoxin units (EU), which a COA converts to EU per milligram of peptide.
“Endotoxin tested” says a test was run. The useful part is the line itself: the method, the value and the specification it was compared against.
Key Facts
- What endotoxin is: lipopolysaccharide (LPS) from the outer membrane of Gram-negative bacteria
- Size: one LPS molecule is about 10–20 kDa, and in water it forms much larger aggregates
- Stability: survives normal sterilizing conditions; dry heat of 250°C for more than 30 minutes inactivates it
- Unit: 1 EU ≈ 0.1 ng of reference endotoxin (EC-5)
- Test methods: LAL gel-clot, kinetic turbidimetric, kinetic chromogenic; rFC fluorescence (USP <86>, official May 2025)
- Reported on a COA as: EU/mg, with the method and the specification
- Not visible by: HPLC purity or mass spectrometry
- Status: CoreVionRX peptides are for laboratory research use only
What Are Endotoxins in Peptides?
Endotoxins are lipopolysaccharides, large molecules that make up much of the outer membrane of Gram-negative bacteria such as E. coli. They are released when bacteria grow or break apart, and they stay active after the bacteria are dead.
A single LPS molecule weighs about 10–20 kDa, and in water these molecules cluster into much larger aggregates. Endotoxin is also very stable: it survives normal sterilizing conditions and wide pH swings. A review of removal methods gives dry heat of 250°C for more than 30 minutes, or 180°C for more than 3 hours, as the conditions that inactivate it (Magalhães et al., 2007).
Most short research peptides are made by chemical solid-phase synthesis, not grown in bacteria. In that case endotoxin usually comes from the process around the peptide: water, buffers, glassware, purification columns and handling. Recombinant proteins made in E. coli start with a far larger endotoxin load, which is why most of the published work on endotoxin artifacts involves them.
Why HPLC Purity Doesn’t Show Endotoxin
HPLC purity measures how much of the UV signal comes from the target peptide compared with related impurities such as shortened or modified sequences. It answers “how much of this is my peptide?” Mass spectrometry answers a second question: “is it the right molecule?”
Neither test is built to see endotoxin. The amounts involved are tiny: 1 EU is about 0.1 ng of reference endotoxin, so 1 EU/mg works out to roughly 0.00001% of the sample by mass. A peptide can read 99% pure by HPLC and still carry endotoxin, because the two numbers measure different things.
That is why endotoxin needs its own assay and its own line on the COA.
Peptide Endotoxin Testing Methods: LAL and rFC
Peptide endotoxin testing uses one of two reagent families. LAL comes from horseshoe crab blood cells and reacts to endotoxin through an enzyme cascade. rFC is a recombinant, non-animal version of the first enzyme in that cascade.
| Method | What it reads | Output |
|---|---|---|
| Gel-clot (LAL) | Whether a firm gel forms | Pass/fail at the reagent’s labeled sensitivity (λ, for example 0.03 EU/mL) |
| Kinetic turbidimetric (LAL) | How fast the sample turns cloudy | A number, read from a standard curve |
| Kinetic chromogenic (LAL) | How fast a yellow color develops | A number, read from a standard curve |
| Recombinant Factor C (rFC) | A fluorescent signal | A number, read from a standard curve; covered by USP <86> |
Whatever the method, a valid test also shows that the sample itself does not distort the reading. The lab spikes a known amount of endotoxin into the diluted sample, and recovery must fall between 50% and 200%. Below 50% means the sample inhibits the reaction; above 200% means it enhances it. Peptides with strong charges or extreme pH sometimes need extra dilution to pass this check.
Eli Lilly scientists validated an rFC method on several pharmaceutical products and reported it equivalent or superior to the compendial test (Bolden and Smith, 2017). USP approved its recombinant-reagent chapter, <86>, in July 2024, and it became official in May 2025.
Peptide Endotoxin Levels: How to Read EU/mg
Peptide endotoxin levels are measured in solution, in EU/mL, and then divided by how much peptide that solution held. The formula is simple: EU/mg = EU/mL ÷ sample concentration in mg/mL.
| Measured | Sample concentration tested | Reported on the COA |
|---|---|---|
| 0.05 EU/mL | 1 mg/mL | 0.05 EU/mg |
| 0.05 EU/mL | 0.5 mg/mL | 0.1 EU/mg |
| Below 0.005 EU/mL (the lowest standard) | 0.1 mg/mL | <0.05 EU/mg |
A value written with “<” means nothing was detected down to the test’s lowest point at that dilution. It is a detection limit, not a measured amount, so two COAs showing “<0.05” and “<0.5 EU/mg” can describe equally clean lots tested at different dilutions.
There is no single official endotoxin limit for research peptides. Pharmacopeial limits apply to finished medicines and are set product by product. For research material, the COA states its own specification (for example “<1 EU/mg”) and whether the lot met it. For comparison, most suppliers of recombinant proteins guarantee less than 1 EU per microgram of protein (Schwarz et al., 2014).
How to Read a Peptide COA
A peptide COA is the lab report for one production lot. Read it top to bottom and check each line against the vial in front of you.
| COA line | What to check |
|---|---|
| Product and lot number | Same name, size and lot number as the vial label |
| Lab and report date | Who ran the tests and when |
| Appearance | Usually white to off-white lyophilized powder |
| HPLC purity | A percentage with its chromatogram and the specification (for example ≥99%) |
| Mass spec identity | Observed mass matches the expected mass for the sequence |
| Endotoxin | Method (LAL or rFC), value in EU/mg and the specification |
| Sign-off | An authorizing signature or approval |
Some COAs add water content, net peptide content or the salt form (acetate or trifluoroacetate). These explain why the weighed powder is not 100% peptide, and they matter when you calculate concentrations.
Keeping Endotoxin Out During Lab Prep
A clean lot can pick up endotoxin on the bench. Most of the risk comes from water and labware, so lab prep focuses on both:
- Dissolve lyophilized powder in sterile water or bacteriostatic water labeled endotoxin-free or pyrogen-free.
- Use sterile, endotoxin-free tubes and pipette tips. Ordinary autoclaving does not remove endotoxin; depyrogenated glassware is dry-heated, typically at 250°C for more than 30 minutes.
- Do not count on a 0.22 µm filter. It removes bacteria, but endotoxin molecules and small aggregates can pass through.
- Keep vials closed, work in a clean hood and label each solution with the lot number and date.
For storage temperatures and shelf life, see the peptide storage guide.
What Published Studies Examined
These studies looked at endotoxin as a source of error in laboratory research. They are listed with their study type.
- Mouse genetics study: Poltorak et al., 1998 (Science) found that two mouse strains that do not respond to LPS carry mutations in the Tlr4 gene, identifying Toll-like receptor 4 as the cell receptor for endotoxin.
- Cell study (mouse macrophages): Gao and Tsan, 2003 (J Biol Chem) compared two recombinant Hsp70 preparations. The one carrying 0.2 ng LPS per µg triggered TNF-α release; the purer one, at 1.4 pg/µg, did not. Removing the LPS with polymyxin B removed the effect.
- Cell study (human macrophages): Luong et al., 2012 (J Inflamm) found that the response to recombinant HSP70 needed both the contaminating endotoxin and the intact protein.
- Cell study (human primary cells): Schwarz et al., 2014 (PLoS One) measured endotoxin in commercial recombinant proteins and found levels in the range stated on their data sheets, plus some higher. Human CD1c+ dendritic cells were activated by LPS amounts equivalent to the contamination found in some of those proteins.
- Review: Magalhães et al., 2007 (J Pharm Pharm Sci) summarized endotoxin chemistry and removal methods: adsorption, two-phase partitioning, ultrafiltration and chromatography.
- Method validation: Bolden and Smith, 2017 (PDA J Pharm Sci Technol) validated rFC on pharmaceutical products as an alternative to LAL.
The common thread: in sensitive cell assays, a small endotoxin load can look like an effect of the material being studied. None of these studies tested a CoreVionRX product.
Standards and Regulatory Status
USP chapter <85> is the compendial bacterial endotoxins test using LAL. USP chapter <86> adds recombinant reagents (rFC and recombinant cascade reagents); USP approved it in July 2024 and it became official in May 2025. The FDA’s guidance Pyrogen and Endotoxins Testing: Questions and Answers, first published in 2012 and reissued as Edition 2 in March 2026, explains how the FDA applies these tests to regulated products.
These standards govern medicines and medical devices. Research peptides are not FDA-approved drugs, and labs that report endotoxin on a research COA borrow the same methods. CoreVionRX peptides are sold for laboratory research use only.
Endotoxin Testing and the CoreVionRX COA
Every CoreVionRX order ships with the certificate of analysis for its lot. CoreVionRX lists three lot tests: purity by RP-HPLC, identity by LC-MS/MS and endotoxin by LAL assay. When your order arrives, match the lot number on the vial to the COA and read the endotoxin line the way this guide describes: method, value in EU/mg and specification.
Compound-specific guides walk through each COA in more detail: BPC-157 10mg, KLOW 80mg, GLOW 70mg, GHK-Cu 100mg, Epitalon 10mg and CJC-1295 + Ipamorelin 10mg.
KLOW 80mg · lot-specific COA included with every order
Frequently Asked Questions
What are endotoxins in peptides?
Endotoxins are lipopolysaccharides (LPS) from the outer membrane of Gram-negative bacteria. In a synthetic peptide they usually come from the process around it, such as water, buffers, glassware and handling, rather than from the peptide itself. They are measured with an LAL or rFC assay and reported in EU/mg.
If a peptide is 99% pure, does that mean it has no endotoxins?
No. HPLC purity compares the target peptide with related peptide impurities; it cannot see endotoxin. 1 EU is about 0.1 ng, so 1 EU/mg is roughly 0.00001% of the sample by mass. Endotoxin needs its own test and its own line on the COA.
What endotoxin level is acceptable for research peptides?
There is no single official limit for research peptides; pharmacopeial limits apply to finished medicines and are set product by product. A research COA states its own specification, for example <1 EU/mg, and whether the lot met it. A value written with “<” is a detection limit, not a measured amount.
What is the difference between LAL and rFC endotoxin testing?
LAL is made from horseshoe crab blood cells and can be run as gel-clot, kinetic turbidimetric or kinetic chromogenic tests. rFC is a recombinant, non-animal version of Factor C, the first enzyme in the LAL cascade, read by fluorescence. USP chapter <86> covers rFC and became official in May 2025.
Does a 0.22 µm filter remove endotoxin?
Not reliably. A 0.22 µm filter removes bacteria, but endotoxin molecules (about 10–20 kDa each) and small aggregates can pass through. Endotoxin is also heat-stable: dry heat of 250°C for more than 30 minutes is used to inactivate it on glassware.
Where can peptides be tested for endotoxin?
Contract testing labs run bacterial endotoxin tests under USP <85> (LAL) or <86> (recombinant reagents). Send the sample with its exact concentration, and ask for the method, the lowest standard on the curve and the spike recovery, which must fall between 50% and 200% for a valid test.
Related Research Guides
- BPC-157 10mg research guide
- KLOW 80mg research guide
- GLOW 70mg research guide
- GHK-Cu 100mg research guide
- Peptide storage guide
Written by the CoreVionRX Research Team. Sources: the PubMed records linked above, USP chapters <85> and <86>, and the FDA guidance linked above.
For laboratory research use only. Not for human or veterinary use.
