Purity Is Not Content: What a Peptide Test Report Can and Can't Tell You

A peptide report that says 99% purity sounds like the end of the conversation. It is not. Purity answers one question. Whether the vial holds the amount on the label, whether it carries endotoxin, and whether trace metals came along are three other questions, and each needs its own test.

What each test answers

Test	What it checks	What it can't tell you
Purity HPLC (high-performance liquid chromatography)	What share of the detected peptide signal is the target peptide	Amount in the vial, endotoxin, metals
Identity LC-MS (liquid chromatography with mass spectrometry)	Whether the molecule has the mass of the intended peptide	The amount in the vial
Amount in the vial net peptide content, in mg	How much peptide the vial holds compared with the label	Contaminants
Heavy metals ICP-MS	Trace lead, arsenic, cadmium and mercury, down to parts per billion	Identity, endotoxin
Endotoxin LAL (Limulus amebocyte lysate assay)	Bacterial endotoxin, in EU/mg (endotoxin units per milligram)	Identity, purity, amount

The one that surprises people is endotoxin. Endotoxin is a fragment of bacterial cell walls. It is active at nanogram amounts and switches on inflammatory signaling in cells through an immune receptor called TLR4. In a cell culture or animal experiment, that alone can change your results, and no purity number will warn you.

What that looks like on a real report

Our CJC-1295 (no DAC) batch 2618CJC5 was tested by Janoshik Analytical in Prague, an independent lab. The vial is labelled 5 mg. The report lists 4.74 mg of peptide and a purity of 99.638%. Two numbers, two different questions. See it and others on our CoA page.

How we label what was tested

We don't claim one blanket test for every product. Purity, identity and amount are run for the peptides we test; heavy metals are added for chemically made (SPPS) peptides; endotoxin is run for biologically produced peptides such as HGH, hCG and IGF-1 LR3, and on request. Each product page shows which reports exist for that batch, and where one isn't published yet, the page says "on request" instead of showing one.

Can a vial be 99% pure and still hold the wrong amount?

Yes. Purity is a ratio inside the sample, not the total amount. A vial can be 99% pure and hold 3 mg when the label says 5. The freeze-dried powder also contains counterions (salt partners such as TFA or acetate) and residual water, so the peptide mass is lower than the weight of the powder.

What is endotoxin, and why can't purity testing see it?

Endotoxin is lipopolysaccharide from the outer membrane of gram-negative bacteria. It can enter through water, buffers or handling, and is a particular risk for peptides made in bacteria such as E. coli. The LAL assay reports it in EU/mg, far below what a purity chromatogram can register.

Why do synthetic peptides get tested for heavy metals?

Solid-phase peptide synthesis (SPPS) uses solvents, TFA cleavage steps and stainless steel equipment that can leave trace lead, arsenic, cadmium and mercury. ICP-MS detects these at parts per billion. One exception: GHK-Cu contains copper on purpose, so a copper reading there is expected.

How can I tell a test report is genuine?

Check that the report names the lab, the client and the batch number, and that the batch matches your vial. Janoshik reports carry a unique key that can be entered at janoshik.com/verify.

For laboratory research use only. Not medical advice.

Verify a batch →