Why contamination is a separate question
Purity and identity testing look at the compound and its close relatives. Endotoxin is a large lipid-and-sugar molecule, metals are single elements, and microbes are living cells; none of them show up as a peptide peak. A sample can be very pure by HPLC and still carry any of the three, which is why they are tested separately.
Endotoxin
Endotoxins are lipopolysaccharides from the outer membrane of gram-negative bacteria. They are heat-stable and can remain in a material after the bacteria themselves are gone, so a sterile product isn't automatically endotoxin-free. In laboratory work they matter because trace amounts can activate immune cells in culture and skew the results of cell-based and in vitro assays. That is why labs check reagents for them.
The standard test is the Limulus amebocyte lysate (LAL) assay, described in USP <85>, run as a gel-clot, turbidimetric or chromogenic method. Some labs use a recombinant factor C assay instead. Results are reported in endotoxin units per milliliter (EU/mL) of the test solution.
Reading the result
- A "<" value means the result was below the lowest level the method can detect. It is a detection limit, not a measurement of zero.
- "NMT" stands for "not more than", the specification the result was checked against.
- The method (LAL, USP <85>) should be named next to the figure.
Sterility
A sterility test checks whether viable microorganisms are present. The traditional method, USP <71>, incubates the sample in growth media for about two weeks and watches for any growth. Faster screens use PCR to look for microbial DNA. Either way, a passing result reads as "no growth" or "not detected".
Lyophilized peptides are normally sterile-filtered as a solution before they are freeze-dried, and a sterility result confirms that step for the lot that was sampled.
Heavy metals
Heavy-metal testing measures elemental impurities that can enter a product from reagents, equipment or catalysts used in synthesis. The four most commonly reported are lead, arsenic, cadmium and mercury. Labs measure them by inductively coupled plasma mass spectrometry (ICP-MS), following USP <232> and <233>.
- "Not detected" means each element was below the method's detection limit.
- "Below limits" means the elements were measured and came in under the specification.
The Adulterant Screen
Some reports add an immunoassay that checks the sample for undeclared substances that have no place in a research compound. A clean result reads "not detected". Like every other screen, it applies only to the lot that was tested.
Reading screening results honestly
- Count a screen as run only when its row appears on the report
- Check that each result names its method
- Read "<" values as detection limits, not zero
- Confirm the screening applies to the same lot as the purity result
Some reports state outright that they exclude a test, such as endotoxin. A vendor shouldn't describe a lot as screened for something its report didn't run. To see a report that ran the full panel, open the Semax certificates or the GHK-Cu certificates in the Lumina Labs COA Library.
Lumina Labs supplies research compounds for in vitro laboratory research use only. They are not intended for human or veterinary consumption, or to diagnose, treat, cure or prevent any disease. These statements have not been evaluated by the FDA.