Purity, Sterility, Endotoxin & Contamination

Four words that are frequently confused or used interchangeably in marketing. They measure different things, and each is an incomplete picture of product quality.

Educational research-literacy content only. Not medical advice, not dosing guidance, not sourcing advice, and not a protocol for human or animal use. See our responsible information policy.

Purity

Purity is the fraction of the labelled compound in the material — for peptides, typically measured by HPLC and expressed as area-percent. High purity (e.g. 99%) means the material is mostly the intended compound. It does not tell you what the other 1% is.

Sterility

Sterility is the absence of viable microorganisms (bacteria, fungi, spores). It is a microbiological measurement, not a chemical one. A compound can be chemically pure and microbiologically contaminated.

Endotoxin content

Endotoxins are heat-stable lipopolysaccharide fragments from Gram-negative bacteria. They survive sterilisation and can trigger severe febrile and inflammatory responses. Pharmaceutical-grade material is tested for endotoxin content (typically Limulus Amebocyte Lysate, LAL). Research-grade material usually is not.

Contamination

Beyond microorganisms and endotoxin, a compound may contain residual solvents, synthesis by-products, heavy metals, or excipients not listed on the label. Pharmaceutical-grade processing controls these explicitly. Research-grade processing does not always.

Why ‘99% pure’ is not the safety claim it sounds like

Many vendor pages stop at the purity number. From a quality-and-safety perspective, the relevant questions are:

• What is the 1% that is not the labelled compound?
• Was the material handled aseptically?
• Has it been tested for endotoxin?
• Have residual solvents been quantified?
• Has the lot been independently tested?

None of these are usually answered for a research-grade peptide. That is one of several reasons we do not treat “research grade” as a safe category for any kind of administration. See: why research grade is not safe.