HPLC and Mass Spectrometry Peptide Testing: A Buyer's Guide
Published: 2026-08-03 · Last updated: 2026-08-03
Every reputable research peptide comes with a Certificate of Analysis that lists at least two tests: HPLC for purity, and mass spectrometry (mass spec, MS) for identity. If you've never looked at a chromatogram or a mass spectrum before, the raw output can look intimidating. This guide walks through what each test measures, what a good result looks like, and how to read the numbers on a CoA without needing a chemistry degree.
What is HPLC and what does it measure?
HPLC is short for High Performance Liquid Chromatography. In plain terms: you dissolve a sample in a solvent, push it through a long thin column under pressure, and the different molecules in the sample move through the column at different speeds. You measure what comes out the other end over time, and you get a graph with peaks — one peak per distinct molecule.
For a research peptide, the ideal chromatogram is one big peak that dwarfs everything else. If the target peptide accounts for 99% of the area under all the peaks, the peptide is 99% pure. The other 1% is impurities: shorter fragments, deletion sequences, salt residue, or side products from synthesis.
On a CoA, the HPLC section will usually show a number ("Purity: 99.2%") and often a thumbnail of the chromatogram itself. If you can see the chromatogram, look for a single dominant peak. A lot of small extra peaks means more impurity, even if the headline number looks fine. If a vendor only shows the number and no chromatogram, they're skipping the interesting evidence.
What is mass spec and what does it measure?
Mass spectrometry is a weighing technique. The instrument ionises the sample, accelerates the ions through a magnetic or electric field, and measures their mass-to-charge ratio. Every peptide has a specific theoretical molecular weight you can calculate from its amino acid sequence. If the mass spec finds a peak at that weight (within the instrument's tolerance, usually a fraction of a Dalton), you have very strong evidence that the molecule in the vial is the one on the label.
A CoA will typically show "Molecular weight (theoretical): 1419.5" and "Molecular weight (observed): 1419.4" — a match within tolerance. Some CoAs include the full mass spectrum image, which is a bar-chart-looking graph with the peak of interest labelled. You don't need to interpret it in detail; you just need the theoretical and observed values to line up.
Mass spec cannot tell you how much of the vial is the target molecule (that's HPLC's job), but it can tell you what the target molecule actually is. If the mass is off by more than a Dalton or two, the peptide in the vial is either a different sequence or a modified form (methylated, oxidised, missing a residue). Ask questions.
Why do I need both tests together?
Because they answer different questions. HPLC tells you how clean the sample is. Mass spec tells you whether the clean thing is the right thing. Missing either one leaves an open question that no other test on the CoA can close.
Consider two failure modes. Failure mode one: a batch tests at 99% HPLC purity, but the mass spec shows the wrong molecular weight. The vial contains a very pure sample of the wrong peptide — maybe a synthesis error, maybe mislabelling. Failure mode two: mass spec confirms the right molecule, but HPLC purity is 70%. The right peptide is present, but it's diluted with a soup of impurities. In one case you're being sold the wrong thing; in the other you're being sold half of the right thing.
A good CoA closes both loops. That's why we run both on every batch and publish both on our methodology page and on the per-product PDPs.
How do I read the numbers on a CoA?
Find these six things on any CoA before you commit to a purchase. Peptide name and sequence: matches the product page and the vial label. Batch or lot number: matches the vial you receive. Test date: recent enough to be relevant (a five-year-old CoA is not useful). Lab name: a real lab with contact information, not "internal QC." HPLC purity: percentage number, ideally with a chromatogram. Mass spec confirmation: theoretical vs. observed molecular weight, ideally with the spectrum.
Extra things you might see: elemental analysis (percent nitrogen, useful for cross-checking peptide content), water content (Karl Fischer titration, tells you how much of the vial weight is residual water rather than peptide), residual solvents, and acetate or TFA counterion content. These are nice-to-haves and matter more for sensitive applications.
If a CoA is missing any of the six core items, treat it as incomplete. If it's a template with blanks or "N/A" in the batch field, it's not a real CoA and the vendor is asking you to trust marketing copy.
What's a red flag on a CoA?
A few dead giveaways of a fake or lazy CoA: no batch number, or a batch number that clearly doesn't match the vial. No test date, or a date years old. A lab name you can't find on the internet, or "in-house QC" with no third-party involvement. HPLC "purity 99%" with no chromatogram image at all. Mass spec "confirmed" with no theoretical or observed weight listed.
More subtle tells: a chromatogram thumbnail so small you can't see the peak shape. A CoA with the vendor's branding but the lab's name absent — it should be the lab's letterhead, with the vendor as the client. Inconsistent fonts on the same page (sign of a template that's been edited by hand). Numbers that are suspiciously round (every batch reporting exactly 99.0% is either extraordinary luck or a rounded default).
The CoA verification guide covers the four-step process for cross-referencing a certificate against the vial in your hand.
Do I need to worry about other tests?
For most research applications, HPLC + MS covers 95% of what you need to know. A few situations call for more. If you're using the peptide in a cell-culture assay, ask about bacterial endotoxin testing (LAL) — even trace endotoxin can crash cell viability. If you're using large quantities in an animal model, heavy metals and residual solvent testing become more relevant. If the peptide is being used in an analytical method development context, water content matters because it affects how you calculate the mass per vial.
For the average buyer, though, HPLC + MS is the right bar. A vendor that runs both on every batch, publishes the CoAs, and links them from the product page has done the important work. Everything else is icing on a cake that already tastes fine.
Questions Canadian buyers ask
What is a good HPLC purity number for a research peptide?
For a well-made research peptide, expect 98% or higher on HPLC purity. Some vendors advertise "99% pure" as a headline number — that's fine as long as the batch-specific CoA backs it up. Anything below 95% is either an unusual peptide (some blends and glycopeptides genuinely test lower) or a manufacturing problem you should ask about.
What does mass spec actually prove?
Mass spectrometry weighs the molecule. Every peptide has a specific molecular weight based on its amino acid sequence. If the mass-spec result matches the theoretical weight of your peptide within a small tolerance, you have strong evidence that the molecule in the vial is the one on the label. It doesn't tell you purity, but it tells you identity.
Why do I need both HPLC and mass spec?
They answer different questions. HPLC tells you how much of the vial contents is one thing versus other things — high purity. Mass spec tells you what that one thing actually is — correct identity. A vial can be 99% pure of the wrong molecule, or the right molecule at only 80% purity. You want both boxes checked.
Can a vendor fake a CoA?
Technically yes — a PDF is a PDF. In practice, faking a CoA that stands up to scrutiny means faking a real lab's letterhead, a real analyst signature, and a real batch number and date sequence. It happens, but the more experienced buyers you talk to, the more they can spot the tells: sketchy fonts, missing lab contact info, chromatogram graphs that were clearly ripped from a textbook. Cross-referencing with the lab directly is the ultimate check.
What lab tests are worth paying extra for?
Bacterial endotoxin testing (LAL) is worth asking about if the peptide is destined for cell culture — endotoxin contamination will kill your cells before the peptide has a chance to do anything. Elemental impurity testing (heavy metals) is a nice-to-have for bulk purchases. Most research applications get by with HPLC + MS, but the more sensitive the downstream assay, the more supplementary testing helps.