For laboratory research purposes only. Not for human consumption.
A Certificate of Analysis (COA) is the single most useful document in research-peptide procurement, and it is also the most commonly misread. A vendor can print “99% pure” on a product page in seconds; a COA is supposed to be the evidence behind that number. But a COA is only as good as the laboratory that produced it, the methods it documents, and whether the lot it describes is actually the lot in your hand. This guide walks through how to read each section of a peptide COA, how to confirm a third-party report such as one from Janoshik Analytical is genuine, and the red flags that should stop a purchase order. It is written for laboratory procurement and quality-control evaluation, not as a protocol for any human or animal use.
What a COA Is, and Why It Matters for Research Procurement
A Certificate of Analysis is a document that records the analytical testing performed on a specific batch of material and the results of that testing. For a synthetic research peptide, a competent COA answers three independent questions:
- Is it the right molecule? (identity, confirmed by mass spectrometry)
- How much of the sample is that molecule versus impurities? (purity, measured by HPLC)
- How much of the dry mass is actually peptide versus water and salts? (content: net peptide content, water, counter-ion)
Those are three separate measurements. A common procurement error is to treat a high HPLC purity figure as the whole story. A sample can be 99% pure and still be the wrong molecule entirely. Purity tells you how clean the main peak is, not what the main peak is. That is why identity and purity are reported separately, and why a COA missing either one is incomplete.
For a research group, the COA also serves a documentation function: it is the record you keep so that, if an experiment produces an anomalous result, you can rule out (or confirm) starting-material quality as a variable. Procurement records that cite the lot number and the testing laboratory are part of good laboratory housekeeping.
How to Read HPLC Purity (and the Chromatogram)
High-Performance Liquid Chromatography (HPLC) is the workhorse method for peptide purity. The instrument separates the components of a sample as they pass through a column, and a UV detector, typically set around 210–220 nm where the peptide bond absorbs, records each component as a peak. Purity is reported as the area of the main peak expressed as a percentage of the total area of all detected peaks.
What to look for on the COA:
- The purity percentage itself. For research-grade peptides, a purity of 98% or higher is the generally accepted benchmark, and 99%-plus is achievable and increasingly common among quality suppliers. Treat unusually round or suspiciously perfect numbers (an exact “100.00%”) with scepticism, since real chromatography rarely produces them.
- The chromatogram, not only the number. A genuine COA includes the actual chromatogram: a trace with a dominant main peak and a clearly marked retention time. Look at the baseline. A clean baseline with one tall, sharp peak and only minor satellite peaks is what high purity looks like. A noisy baseline, several large peaks of comparable height, or a main peak with heavy “shoulders” tells a different story than the headline figure.
- The method line. Better COAs state the column, mobile phase, gradient, and detection wavelength. You do not need to reproduce the method to benefit from seeing it; its presence signals a real analytical run rather than a fabricated value.
If a product page advertises a purity figure but the COA shows no chromatogram at all, only a typed number, you have a claim, not evidence.
How to Read LC-MS Identity (Observed vs Theoretical Mass)
Mass spectrometry (MS), usually run as LC-MS (liquid chromatography coupled to mass spectrometry), answers the identity question. Every peptide has a molecular formula, and from that formula you can calculate a theoretical (expected) monoisotopic or average mass. The mass spectrometer measures the actual mass of the molecule in the sample. The two should match.
Reading the MS section of a COA:
- Find the theoretical mass and the observed mass. The COA should state both: the calculated mass for the named peptide and the mass the instrument actually measured. They should agree within the normal tolerance of the instrument (on the order of about ±1 Da for the typical resolution used in routine peptide QC). A close match is the confirmation that the main HPLC peak is the peptide it is supposed to be.
- Watch for multiply-charged ions. Peptide mass spectra frequently show the molecule carrying more than one charge, so you may see peaks at the mass divided by 2, 3, and so on (often labelled [M+2H]²⁺, [M+3H]³⁺). A competent COA either reports the deconvoluted neutral mass or labels the charge states. This is normal and is not a discrepancy.
- A mismatch is disqualifying. If the observed mass does not correspond to the named compound (after accounting for charge state and any expected salt form), the material is not what the label says, regardless of how clean the HPLC purity looks.
Identity by MS and purity by HPLC are complementary: HPLC says “the sample is clean,” MS says “the clean thing is the right thing.” You want both.
Lot-Number Matching
This is the step most likely to be skipped and the one that quietly defeats the entire purpose of a COA. The lot (batch) number on the COA must match the lot number printed on the vial you received. A COA describes one specific batch of material. A report from a different batch, even of the same compound from the same vendor, tells you nothing about what is in your vial.
When a shipment arrives:
- Read the lot/batch number on the physical vial label.
- Confirm it appears, character-for-character, on the COA.
- Confirm the compound name and any stated mass/strength on the vial match the COA.
If a vendor supplies a single “representative” COA that is reused across many batches, or a COA whose lot number does not appear on your vial, the document is not certifying your material. Lot mismatch is one of the clearest reasons to query an order before using it.
Other Parameters: Net Peptide Content, Acetate, Water, Endotoxin
Beyond purity and identity, a fuller COA may report several content and contamination parameters. These matter most for quantitatively sensitive or biologically sensitive research.
- Net peptide content (peptide content). Purity describes the main peak relative to other peaks; net peptide content describes how much of the total dry mass is actually peptide, as opposed to bound water and counter-ions. It is typically determined by amino acid analysis or elemental analysis. Because lyophilised peptides carry salt and moisture, net peptide content is commonly well below 100%, with figures in the rough range of 70–90% typical depending on the peptide. For any research that depends on knowing the precise quantity of peptide present, this is the figure to use, not the gross powder mass.
- Counter-ion / acetate (or TFA) content. Synthetic peptides are usually isolated as a salt. Acetate and trifluoroacetic acid (TFA) are the two most common counter-ions, measured by ion chromatography. Peptides rich in basic residues (such as arginine) bind more counter-ion. This value links directly to net peptide content, since salt is part of what makes the powder weigh more than the peptide alone.
- Water content. Lyophilised peptides are hygroscopic; residual water is typically measured by Karl Fischer titration. Like counter-ion content, it explains the gap between powder mass and peptide mass.
- Residual solvents. Trace solvents from synthesis and purification are determined by gas chromatography. Relevant where solvent artefacts could interfere with downstream assays.
- Endotoxin / bioburden, where relevant. For cell-culture or small-animal research, endotoxin (measured by LAL assay) and microbial limits matter, because contamination can confound biological readouts. These are not part of a basic identity-and-purity COA; if your protocol is sensitivity-limited, request them explicitly before ordering rather than assuming they were run.
Not every COA reports every parameter, and that is normal: a routine third-party identity-and-purity report centres on HPLC and MS. The point is to know which parameters your specific research requires and to confirm they are present rather than inferred.
How to Verify a Third-Party Report Is Genuine
The strongest COA is one issued by an independent laboratory with no commercial relationship to the manufacturer or vendor: a lab that is not owned by, operated by, or co-located with the supply chain it is testing. In the European research-peptide market, Janoshik Analytical, an independent analytical laboratory based in Prague, Czech Republic, has become one of the most widely referenced third-party testing labs for this purpose.
The reason independent testing is verifiable at all is that the report carries a unique reference, and the lab publishes a way to look it up:
- Use the verification page. Janoshik operates a public verification page at janoshik.com/verify/. A buyer enters the report’s task number and unique key and the page returns the original record held by the laboratory: the compound name, the purity result, the molecular-weight data, and the test date. You then compare those values against the COA the vendor gave you. If the portal’s record matches the PDF, the report is authentic and unaltered.
- Match every field, not only the headline. Verification is only meaningful if you check that the compound, purity, mass, and date on the vendor’s document agree with the laboratory’s own record. A forged or edited PDF can copy a real-looking layout; it cannot change what the lab’s database returns for that reference.
- Understand what a failed lookup means. If a reference does not verify, the most common explanation is a mistyped key, so re-enter it carefully. Beyond that, a genuine failure points to either a document that was never issued by the lab or one that has been altered. Either way, an unverifiable third-party report should be treated as no report.
- When in doubt, contact the laboratory. If you cannot resolve a report through the portal, the appropriate step is to contact the issuing laboratory directly to confirm whether they tested the referenced sample. An independent lab can confirm or deny that a report is theirs; the vendor cannot vouch for that on the lab’s behalf.
One important limitation to keep in perspective: a third-party laboratory tests the sample that was submitted to it, not every vial in a production batch. Verification confirms that a genuine test was performed on a representative sample and that the report is authentic. It is strong evidence of quality and honesty, not an individual per-vial guarantee. That is a normal property of analytical testing, not a defect, and it is why lot-level consistency and a vendor’s track record still matter alongside the COA.
Red Flags That Should Stop a Purchase Order
A short checklist of warning signs that recur across low-quality suppliers:
- No document at all. “Contact us for the COA” or “tested in-house, certificate on request” with nothing posted is the most basic red flag. A purity claim without a retrievable document is marketing, not evidence.
- In-house-only COA. A certificate on the vendor’s own letterhead, with no independent laboratory named, has an obvious conflict of interest. It may still be accurate, but it is not independent, and it cannot be verified against an outside record.
- Lot mismatch. The lot number on the COA does not match the vial, or a single COA is reused for every batch. The document is not certifying your material.
- Number without a chromatogram. A typed purity percentage with no chromatogram and no mass-spec trace gives you nothing to inspect or verify.
- Identity missing. HPLC purity is shown but there is no mass-spectrometry identity confirmation, so you know the sample is clean but not that it is the right molecule.
- A report that will not verify. A third-party COA whose reference does not resolve on the issuing laboratory’s portal, and which the vendor cannot explain, should be treated as absent.
- Pressure to skip diligence. Any supplier that treats routine COA and verification requests as unreasonable is signalling how it handles quality generally.
None of these checks require specialist equipment, only the document, the vial, and a few minutes at the verification portal. Building them into a standard intake step is inexpensive insurance against wasted experiments and unreliable data.
Summary
A peptide COA earns its place in procurement only when you read all of it: HPLC purity with the chromatogram, mass-spectrometry identity with observed-versus-theoretical mass, the lot number matched to the vial, and, where the research demands, net peptide content, counter-ion and water content, and endotoxin. The decisive layer is independence: a report from an outside laboratory such as Janoshik Analytical can be confirmed through the lab’s own verification page at janoshik.com/verify/, and a report that cannot be verified is, for practical purposes, no report. Treat the document and the verification as one routine step, and the COA stops being a marketing line and becomes what it is meant to be: evidence.
CertaPeptides posts third-party Janoshik COA documents on its product pages and labels all compounds for research use only. No human-use claims are made.
This article is for research information purposes only. All compounds referenced are supplied exclusively as research chemicals for laboratory use, not as medicinal products, and are not intended for human or animal use. Some compounds named (for example semaglutide and tirzepatide) are active substances in separately authorised medicines; CertaPeptides supplies only research-grade chemicals and makes no therapeutic claims.