A Certificate of Analysis is a document that records specific laboratory test results for a single manufactured batch of material. Think of it like a report card that shows a handful of selected grades — it covers the subjects that were tested, but doesn’t capture everything that went into the student’s performance.

A COA reflects the tests a supplier chose to run on a given batch. It is a useful starting point, but it does not describe how the peptide was made, how consistent the manufacturing process was, or whether the molecules are stable and functional.

Not on its own. Purity is an important metric, but it measures chemical similarity — not functional integrity. Understanding what purity does and doesn’t tell you is one of the most valuable things you can take away from this guide.

Purity is most commonly measured using HPLC (High-Performance Liquid Chromatography). HPLC separates compounds based on how long they take to travel through a column — called their retention time. Because structurally similar molecules travel at nearly the same speed, some closely related impurities can co-elute with the target peptide and be counted as part of the pure fraction.

A peptide can be highly pure yet still contain truncated chains, chemically modified residues, or aggregated molecules. Purity confirms the correct material is present — it does not confirm that every molecule in the sample is intact and functional.

This is where understanding the limits of purity testing becomes genuinely useful. Most standard purity tests cannot distinguish between a fully intact, functional peptide and a closely related variant that looks nearly identical in analysis but behaves differently in practice. Common examples include:

Identity confirmation verifies that the expected peptide mass exists in the sample. This is typically performed using mass spectrometry — an instrument that measures the mass-to-charge ratio of molecules and matches what is detected against the theoretical mass of the intended peptide.

Think of it like checking that a package weighs what it should. It confirms something is inside — but it doesn’t open the box to verify that the contents are intact.

There is no universal potency test for peptides. Potency — how effectively a peptide performs its intended biological function — depends on the specific biological target being studied, which means testing must be designed around that context. This is not a gap unique to any one supplier; it reflects the nature of peptide science.

Why potency testing is rarely performed:

• Functional assays must be custom-designed for each specific biological target
• They are technically complex and significantly more expensive than standard COA tests
• Most peptide suppliers do not routinely offer them as part of standard QC panels

Net Peptide refers to the estimated amount of actual peptide by weight in the final product, after all non-peptide components are excluded — things like salts, water, residual solvents, and stabilizers that add weight to the vial but are not the peptide itself.

Think of it like the net weight on a bag of coffee: it tells you how much coffee is inside, not counting the bag, moisture, or any added fillers.

Peptides are structurally sensitive molecules. The way they are made has a direct impact on their quality — sometimes in ways that standard COA testing is not designed to detect. Even well-intentioned process variations can affect the final product.

Stability describes how well a peptide maintains its molecular integrity over time and across different conditions. Even a well-manufactured peptide can degrade during storage, shipping, or handling — and these changes may not be visible on a standard COA.

Endotoxins — also called lipopolysaccharides (LPS) — are structural components of the outer membrane of gram-negative bacteria. They are biologically active even at very low concentrations and are unrelated to peptide purity or molecular identity.

Where do endotoxins come from? They can be introduced during synthesis, purification, or handling — essentially any step involving reagents, equipment, or environments that are not rigorously controlled for microbial contamination. Good manufacturing practices significantly reduce this risk.

The best way to evaluate a peptide supplier is to ask straightforward questions about their process and documentation. Good manufacturers welcome these conversations — they reflect the kind of rigor that serious quality programs are built on.