How to Read a Peptide COA: HPLC Purity, Mass Spec Identity and What a Fake One Looks Like
A certificate of analysis is the only evidence that a research peptide is what the label says. How to read the HPLC chromatogram, how the purity percentage is calculated, why retention time is not identity, what the mass spectrometry section must show, net peptide content, endotoxin and sterility lines, and the red flags of a fabricated report.
A certificate of analysis, or COA, is the document that tells you what is actually in a vial of research peptide: what compound, how pure, and who measured it. Everything else a supplier says is a claim; the COA is the evidence, and only if you can read it. This guide goes through a real one section by section: the HPLC chromatogram and how the purity percentage is calculated from it, why a retention time does not prove identity, what the mass spectrometry result has to show, the lines for net peptide content, water, counter-ion, endotoxin and sterility, and then the specific ways a fabricated or recycled report gives itself away. It is written for anyone buying research peptides in the UK who wants to check a supplier's claim rather than take it on trust, including ours.
What a COA is, and who should have produced it
A COA is a laboratory's record of the tests run on a specific batch and the results obtained. Three things make it worth anything. It is batch-specific: the batch or lot number on the document matches the one on the vial. It names the laboratory: a real analytical laboratory with an address, ideally accredited to ISO/IEC 17025 for the relevant methods, which in the UK means accreditation by UKAS or an equivalent national body abroad. And it is complete: it shows the data, not just a summary line. A one-line "purity 99.2%" with a logo is a claim in a nicer font.
Who produced it matters as much as what it says. A test run by the seller is not independent; the seller has a direct interest in the number. A test run by the manufacturer overseas is better but still one step removed. A test commissioned by the seller from an independent third-party laboratory on the batch they actually received is the standard a careful buyer should look for, because it checks the manufacturer as well as the product.
The HPLC section: what the chromatogram shows
High-performance liquid chromatography separates the components of a sample by pushing it through a column under pressure. For peptides the column is almost always reversed-phase, which separates by hydrophobicity: the more water-repelling the molecule, the longer it clings to the column before eluting. A detector at the column outlet, usually ultraviolet at around 214 to 220 nm where the peptide bond absorbs, records a signal as each component comes off. The plot of signal against time is the chromatogram. The target peptide is the main peak; smaller peaks are impurities, typically truncated or deletion sequences from synthesis, oxidised or deamidated forms, and protecting-group remnants.
A genuine chromatogram has recognisable features. Time runs along the bottom, in minutes; absorbance up the side. The baseline is flat and low. The main peak is sharp and roughly symmetrical. The impurity peaks are labelled with their retention times and their area percentages. The method conditions are stated somewhere on the report: column type and dimensions, mobile phases, gradient, flow rate, detection wavelength, injection volume. Without the conditions, the picture cannot be compared with anything and cannot be reproduced.
How the purity percentage is calculated
The purity figure on a COA is normally area percent: the area under the main peak as a percentage of the total area under all the peaks that count. The pharmacopoeial chapter that defines the procedure, USP <621>, adds conditions that most marketing omits. Peaks from the solvent, the mobile phase or the sample matrix are excluded. Peaks below a stated disregard limit are excluded. And the calculation assumes the detector response is linear over the range of the peaks being compared, an assumption a competent laboratory validates. Area percent also assumes every component absorbs equally at the detection wavelength, which is roughly true for peptides at 214 nm and not true for everything.
The consequence is that "99.2% pure" means "99.2% of the UV-absorbing material that eluted from this column under these conditions, above this threshold, was in the main peak". That is a useful number. It is not the same as "99.2% of the mass in the vial is the stated peptide", which is what a buyer usually hears. The difference is covered by the net peptide content line, below, and our article on what 99% purity actually means goes further into it.
Why retention time is not identity
A common shortcut is to treat a familiar retention time as proof that the right compound is in the vial. The guideline regulators use for drug-substance specifications, ICH Q6A, written for licensed medicines but sound for any peptide certificate, says plainly that identification by a single chromatographic retention time alone is not regarded as specific. Two different molecules can elute at the same time. Retention time shifts with column age, temperature and mobile-phase preparation, so it is only meaningful relative to a reference standard run under identical conditions. HPLC tells you how pure the sample is. It does not tell you what it is.
The mass spectrometry section: what it must show
Identity comes from mass spectrometry. The instrument ionises the sample and measures the mass-to-charge ratio of the ions; for a peptide, electrospray ionisation typically produces several charge states, written [M+H]+, [M+2H]2+ and so on, and the observed values are converted back to a molecular mass. A complete COA reports the observed mass and the theoretical mass calculated from the sequence, and they agree within a stated tolerance, commonly a fraction of a dalton on a high-resolution instrument and around half a dalton on a lower-resolution one. ICH Q6A accepts a combined technique such as HPLC with mass spectrometry as specific identification, which is exactly why a proper COA pairs the two.
You can check the theoretical mass yourself. Enter the sequence into the molecular weight calculator on this site and compare the result with the figure on the report; a mismatch of more than a dalton or two, once you have allowed for the average-versus-monoisotopic convention the laboratory used, needs an explanation. Tandem MS, which fragments the peptide and reads the sequence from the fragment ladder, is the gold standard for confirming sequence and is sometimes but not always included in commercial COAs.
The other lines that matter
What each COA line tells you and why it matters Line on the COA What it measures Why a buyer should care Appearance Visual description of the lyophilised cake or powder A first check against the vial you received Net peptide content Fraction of the gross mass that is actually peptide, after counter-ion and water The label mass is gross; net content, often 60 to 90%, is what you calculate concentrations from Water content (Karl Fischer) Residual water in the lyophilisate High water shortens shelf life and inflates gross mass Counter-ion (TFA or acetate) The salt form left over from purification TFA can interfere with some cell assays; acetate exchange is sometimes specified Bacterial endotoxin (LAL) Endotoxin in EU/mg Endotoxin wrecks cell-based assays; a limit should be stated Sterility Whether the vial contents are sterile Rarely tested for research grade; absence of the line means untested, not sterile Amino acid analysis Composition check by hydrolysis Independent confirmation of content; optional but reassuring
Not every research COA carries every line, and a shorter certificate is not automatically dishonest. It is a shorter certificate, and what it does not say, it does not say. A buyer who needs endotoxin data for a cell assay should not infer it from a purity figure.
The red flags of a fabricated or recycled COA
No batch or lot number, or a number that does not match the vial. This alone disqualifies the document. A purity percentage with no chromatogram, or a chromatogram with no method conditions. The same chromatogram image on several products or several batches. Real batches differ. A chromatogram that is too perfect: a single peak on a flat line with no impurity peaks at all, at a stated purity below 100%. No mass spectrometry, or an observed mass with no theoretical mass to compare it with. A laboratory name with no address, no accreditation number, or one that does not exist when you look it up. A "COA" that is a supplier's own letterhead with a table of results and no laboratory named. That is a self-declaration, not a certificate. A vague reference to "USP standards" or "GMP" with no method, chapter or certificate behind it. A date that precedes the compound being offered, or one document reused for years. Our guide to counterfeit peptides sets out how substituted and under-filled products get into the market and why a forged COA is the usual cover for them.
How to check a COA in ten minutes
Match the batch number on the document to the one on the vial. Find the laboratory's name and address, and confirm it exists and does peptide analysis. If it claims accreditation, check the accreditation body's public register. Read the chromatogram: method conditions stated, baseline visible, main peak and impurity peaks labelled with retention times and area percentages. Confirm the purity figure is area percent from that chromatogram and not a number floating on its own. Read the mass spectrometry line: observed mass, theoretical mass, and agreement. Check the theoretical mass against the sequence with the molecular weight calculator. Note the net peptide content if given, and use it for your concentration arithmetic. Ask the supplier for anything that is missing. The speed and completeness of the answer is itself information. Where Vivera Labs stands
Every product page lists the compound, quantity and the manufacturer's listed purity specification, marked as a specification rather than a batch result. We do not yet publish batch certificates of analysis on product pages; original batch reports will be published against the matching product as they are received, and until then we will tell you plainly what we hold for a batch and what is pending. We would rather you read the document and decide than take a percentage on trust, which is why this guide exists. Questions about a specific batch go to contact.
Frequently Asked Questions What is a peptide COA? A certificate of analysis is a laboratory's record of the tests run on a specific batch of peptide and the results: typically HPLC purity, mass spectrometry identity, and sometimes net peptide content, water, counter-ion and endotoxin. It should be batch-specific, name the laboratory, and show the data rather than a summary line.
How is HPLC purity calculated? As area percent: the area under the main peak divided by the total area under all counted peaks in the chromatogram, excluding solvent and matrix peaks and anything below the disregard limit. It describes the proportion of UV-absorbing material in the main peak under those conditions, not the proportion of the vial's mass that is peptide.
Does HPLC prove what the peptide is? No. HPLC measures purity, not identity. Two different molecules can share a retention time, and retention time drifts with conditions. Identity comes from mass spectrometry, where the observed molecular mass is compared with the theoretical mass calculated from the sequence.
What should the mass spectrometry section show? The observed mass of the main peak, the theoretical mass from the sequence, and that they agree within a stated tolerance. Charge states such as [M+H]+ and [M+2H]2+ may be listed. Tandem MS sequence confirmation is the gold standard but is not always included.
What is net peptide content and why does it matter? The fraction of the gross powder mass that is actually peptide once counter-ion salts and residual water are excluded, commonly 60 to 90%. The label mass is gross. Concentrations for quantitative work should be calculated from net content, which is why a good COA reports it.
How can you tell if a COA is fake? No batch number or a mismatched one; a purity figure with no chromatogram; the same chromatogram on multiple products; no method conditions; no mass spectrometry; an unnamed or unfindable laboratory; a supplier's own letterhead presented as a certificate. Any one of these means the document proves nothing.
Is a COA from the seller's own lab acceptable? It is better than nothing and worse than an independent one. The seller has a direct interest in the result. The standard a careful buyer should look for is a test commissioned from an independent third-party laboratory on the batch actually supplied.
Does Vivera Labs publish COAs? Not yet on product pages. Original batch reports will be published against the matching product as they are received; until then we say plainly what we hold for a batch and what is pending.
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