Every compound discussed here is supplied strictly as a laboratory research material. Nothing on this page is approved, intended or authorised for human consumption or any therapeutic use. This article is written for qualified researchers and is not medical advice.
What a Certificate of Analysis actually is
A Certificate of Analysis (COA) is a laboratory document that ties a specific batch of material to the results of the tests run on it. It is not marketing, and it is not a spec sheet describing what the product should be — it is the record of what an analytical lab actually measured for the vials in front of you. A proper COA identifies the compound, the batch or lot number, the testing methods used, and the results those methods returned. Without it, a purity claim is just a number on a website.
The two questions a COA exists to answer are simple: is this the right molecule, and how much of the vial is that molecule versus everything else. Answering those reliably takes two different instruments.
How peptides are tested
Reputable peptide analysis rests on two complementary techniques. One measures purity; the other confirms identity. You want both on a COA.
- HPLC — purity. High-Performance Liquid Chromatography pushes the dissolved sample through a column so its components separate out and elute at different times. The instrument plots a chromatogram of peaks; the target peptide should appear as one dominant peak. Purity is reported as the area of that main peak as a percentage of all peaks combined — so "≥99% by HPLC" means the target accounts for at least 99% of the detected material, with impurities and truncated sequences making up the rest.
- Mass spectrometry — identity. HPLC tells you how much of one thing you have, but not what that thing is. Mass spectrometry (MS) ionises the molecule and measures its mass-to-charge ratio, giving a precise molecular weight. Matching the measured mass against the peptide's theoretical mass confirms you have the correct sequence and not a look-alike. Purity without identity is only half the story.
A sample can be 99% pure and still be the wrong peptide. It can also be the right peptide but only 80% pure, diluted with salts, solvents or failed sequences. HPLC answers "how pure?" and MS answers "is it what it says?" — a credible COA carries results from both.
What ≥99% purity means — and why it matters
When a COA reports ≥99% purity by HPLC, it means less than 1% of the detected material is something other than the target peptide. That remaining fraction is not inert filler — in peptide synthesis it is typically truncated or deletion sequences, residual synthesis reagents, or counter-ions. In research, those impurities are exactly what undermine reproducibility: they can shift potency, confound assays, and make it impossible to know whether an observed effect came from the compound or the contamination.
Higher purity narrows that uncertainty. The difference between 95% and 99% sounds small, but it is a five-fold reduction in impurity load — and when you are trying to attribute a result to a single variable, that matters. This is why serious suppliers test to a ≥99% threshold rather than treating "high purity" as a slogan.
How to actually read a COA
You don't need to be an analytical chemist to sanity-check a certificate. Look for these fields and confirm they are internally consistent:
- Batch / lot number. This must be present and must match the number printed on the vial you received. A COA for a different batch tells you nothing about your material.
- Compound name and, ideally, sequence or CAS. Confirms the certificate is for the peptide you ordered.
- Method. "HPLC" and "MS" should be named explicitly, not implied. A method column with no method is a warning sign.
- Purity %. The headline HPLC result — check it meets the stated threshold and isn't quietly lower than the product page claims.
- Retention time. The time (in minutes) at which the main peak elutes on the chromatogram. Its presence shows the result came from a real run, not a template.
- Measured vs. theoretical mass. On the MS section, the measured mass should sit close to the peptide's theoretical mass. A large mismatch means the identity isn't confirmed.
- Test date and issuing lab. A dated certificate from a named laboratory is far stronger than an undated, unattributed one.
Red flags
Most bad COAs give themselves away quickly. Treat any of the following as a reason to walk:
- No COA at all, or "available on request" that never actually arrives.
- Seller-generated numbers — a purity figure with no chromatogram, no method and no third-party lab behind it is just a claim in a nicer font.
- Mismatched batches — the COA's lot number doesn't match the vial, or the same certificate is reused across every product.
- No retention time, no mass data, no test date — the hallmarks of a template rather than a genuine analytical run.
- Purity claims that beat the COA — a page saying "99%" while the attached certificate reads 96%.
How RS Bio Labs handles it
Every peptide we supply is tested to ≥99% purity by third-party HPLC, with identity confirmed by mass spectrometry. A Certificate of Analysis is included with every order and available on request for any batch — so you can match the paperwork to the vial before it goes anywhere near an experiment. If you want to see how this fits alongside sourcing more broadly, our guide on where to buy Retatrutide in the UK covers what separates a serious supplier from a chancer, and the knowledgebase collects our handling and testing references in one place.
The bottom line
A COA turns a purity claim into something you can verify. Insist on one per batch, check that HPLC purity and MS identity are both present, confirm the batch number matches your vial, and treat missing methods or mismatched lots as disqualifiers. Get that right and your material stops being a variable in your research. You can browse compounds — every one COA-backed — on our Retatrutide UK page and across the full range.