What sterility testing checks
A sterility test incubates a portion of the sample in nutrient growth media under conditions that favor microbial growth, then observes for turbidity or colonies over a defined period. No growth supports a sterile result — meaning no viable, culturable bacteria or fungi were present in the tested material. It is a direct check for living contamination, not a measure of the peptide molecule itself.
Sterility is not the same as endotoxin
This is the distinction researchers most often collapse. Sterility asks whether microbes are alive; endotoxin asks whether bacterial residue is present. Endotoxin (lipopolysaccharide) is a structural fragment of gram-negative bacteria that persists even after the organisms are dead. A sample can pass sterility — no living microbes — and still carry endotoxin from bacteria that were killed during processing. That is precisely why a rigorous panel runs both tests independently.
| Assay | Question it answers | Type |
|---|---|---|
| Sterility | Are viable microbes present? | Microbiological |
| Endotoxin (LAL) | Is bacterial LPS residue present? | Microbiological |
| HPLC purity | How pure is the compound? | Chemical |
| Mass spectrometry | Is it the right molecule? | Chemical |
| Heavy metals | Are metal residues within limits? | Chemical |
Why it matters for research
Microbial contamination is a slow-acting problem. Living organisms can degrade a peptide over time, introduce their own biological activity into an assay, and ruin cell-culture and animal work by adding an uncontrolled variable. Because contamination may not be visible, confirming sterility up front protects both the shelf stability of the reagent and the reproducibility of any experiment that depends on it.
Where it sits on the Ethos Bio panel
Every Ethos Bio lot is independently verified by MZ Biolabs, a third-party analytical laboratory in Arizona, on a five-point panel: RP-HPLC purity, HPLC-MS identity, endotoxin (LAL), heavy metals, and sterility. Each point answers a different question, and all five results travel on the Certificate of Analysis that ships with the vial.
See the full methodology
Read how the five-point panel works end to end, then browse the public COA library to see each result reported per lot.
Frequently asked questions
What does sterility testing confirm?
It confirms the absence of viable, culturable microorganisms — bacteria and fungi — in the sample. A portion is incubated in growth media; no growth over the test period supports a sterile result.
How is sterility testing different from endotoxin testing?
They answer different questions. Sterility asks whether live microbes are present; endotoxin (LAL) measures lipopolysaccharide from gram-negative bacteria, which can remain even after the bacteria are dead. A sample can be sterile yet still carry endotoxin, so both are tested separately.
Does a purity assay cover sterility?
No. HPLC purity and mass-spectrometry identity describe the target molecule, not biological contamination. Sterility is a distinct microbiological assay, which is why a complete five-point COA reports it on its own line.
Why does sterility matter for research reagents?
Microbial contamination can degrade a peptide over time, introduce confounding biological activity into experiments, and compromise cell-culture and animal work. Confirming sterility protects both the integrity of the reagent and the reproducibility of the research.