AKRO Research LibraryAKRO Research store

How to Read a Peptide Certificate of Analysis, Field by Field

By · Published

A certificate of analysis (COA) is a lab’s report of what it measured in one specific lot, so it is best read in order: who tested and whether that lab’s accreditation covers the tests, which lot and which dates, identity by mass spectrometry (a method that measures the mass of the molecules in a sample), purity by HPLC (a method that separates a sample into its components), and then the lines for net peptide content, endotoxin, metals and sterility. The last check is whether the lot on the report is the lot printed on the vial, because a COA says nothing about any other lot.

What does each field on a peptide COA tell you?

Not every COA carries every line. A missing line is not proof of a problem, but it does mean the document is silent on that point.

Field What it tells you What to check
Lab name, address and contact Who produced the numbers A real address and a way to reach the lab that does not run through the seller
Accreditation statement Whether an accreditation body has assessed the lab for a defined set of tests The body’s name, and a scope that lists the tests used
Report identifier A unique number for this report Unique to this report, and one the lab can confirm
Lot number Which production run was tested Identical to the lot on the vial label
Dates When the sample was received, tested and reported In a sensible order
Method The procedure behind each result Named methods, not just the word “tested”
Identity (mass spectrometry) Whether the measured mass matches the expected mass Both masses shown, ideally with the spectrum
Purity (HPLC) The share of detected signal in the main peak The percentage, the detection wavelength and a chromatogram that fits the number
Net peptide content The share of the powder that is peptide Whether the line exists, and the method
Endotoxin Bacterial endotoxin activity Method, units, result and limit
Metals Named elemental impurities Which elements, the method and the limit
Sterility Whether microbial growth appeared in a sterility test Method and result
Authorizing person Who approved the report, and that results apply only to the items tested A named person or signature, and the statement

Who tested it, and does accreditation matter?

ISO/IEC 17025:2017 is the international standard for the competence of testing and calibration laboratories. It describes how a laboratory operates, so it speaks to the lab and not to the product. An accreditation claim tells you something about the lab that did the testing. It tells you nothing about what is in the vial.

Accreditation bodies assess laboratories against the standard, and ILAC is the international organization of those bodies. An accredited lab holds a defined scope covering particular tests, and it may not be accredited for every test it performs. A 2020 article in Quality Progress argued that statements such as “ISO/IEC 17025 compliant” give customers a false sense of security when there is no independent accreditation and no scope that includes the test performed. To check a claim, find the accreditation body named on the report, look the lab up in that body’s public directory, and confirm the scope lists the tests on your COA.

The same standard lists the minimum content of a test report, unless the laboratory has valid reasons for leaving an item out. The list includes the laboratory’s name and address, a unique identification of the report, the method used, a description of the item tested, the dates the work was done and the report was issued, the results with their units, a statement that the results relate only to the items tested, and the person who authorized the report (clause 7.8.2.1). A COA that omits most of these is hard to check, whatever else it shows.

A COA can come from the seller’s own lab or from an outside lab. An outside lab separates the party that makes the product from the party that reports on it, though the seller may still be the one paying for the test. A seller’s own lab may be fully competent, but its competence has to be shown the same way: accreditation scope, named methods and a report identifier it can confirm.

How do I match a COA to the lot on the vial?

Find the lot number on the vial label and on the COA. The characters must be identical, including any letters and dashes. Then check the dates: the sample is received, then tested, then the report is issued, so the dates should not run backwards. A report also states that its results relate only to the items tested, so it says nothing about another lot, even of the same product from the same seller. Treat one COA offered for a whole product line, or the same report identifier on two lots, as a reason to ask questions. If a vial carries a QR code or a web address, follow it and check that the lot number on the page matches the vial.

What does “99% purity” actually mean?

On a peptide COA, purity is usually the HPLC area percent. HPLC (high-performance liquid chromatography) separates the components of a sample and records each as a peak. The purity figure is the area of the main peak divided by the total area of all peaks the detector recorded, multiplied by 100. So 99% means that 99% of the detected signal came from the main peak. It does not mean that 99% of the powder is peptide.

The figure has limits. The detector sees only what responds to it, so water is invisible, and salts and counterions may be invisible or may leave with the solvent at the start of the run, where a report may or may not count them. Impurities that leave the column at the same moment as the main peak are counted as part of it. And the detector does not respond equally to every molecule. A study that measured absorbance at 214 nm, a wavelength at which the peptide bond absorbs light, reported that tryptophan absorbs about 30 times as much light as the peptide bond does, and that phenylalanine, tyrosine and histidine each absorb about six times as much (PMID 17539659). Peptides and impurities with different amino acid compositions therefore give different signals for the same amount of material. A purity figure should come with its detection wavelength and a chromatogram. HPLC vs mass spectrometry for peptides explains how to read both.

Whether a small difference between two purity figures is meaningful depends on how precise the method is, which a validated method reports (ICH Q2(R2)). That guideline is written for commercial drug substances and products, so it is a reference for what validation covers and not a rule for research materials.

How is purity different from net peptide content?

Purity asks how much of the detected peptide-related signal belongs to the right peptide. Net peptide content asks how much of the powder in the vial is peptide at all. A freeze-dried powder can also hold water and counterions, which are the charged partners that accompany a peptide when it is supplied as a salt. Peptides made by solid-phase synthesis and purified with trifluoroacetic acid, for example, are often obtained as trifluoroacetate salts, and the authors of a 2025 study concluded that counterion quantification and specification matter in assays with synthetic peptides (PMID 40872554).

A powder can therefore be 99% pure by HPLC and still be well below 99% peptide by weight, because water and counterions are part of the weight but not of the HPLC figure. An illustrative case is a powder that is 99% pure by HPLC and 80% peptide by weight, with the other 20% made up of water, counterions and other material. The numbers are examples only.

Net peptide content is measured by methods such as amino acid analysis, which breaks a peptide into its amino acids and measures how much of each is present (PMID 19937719). Producers of peptide reference standards report using a mass balance approach to assign a quantitative value to bulk peptide material (PMID 36949371). If a COA gives purity and no peptide content, the second question stays open. That does not make the document wrong.

What do the endotoxin, metals and sterility lines mean?

Endotoxin. Endotoxins are components of gram-negative bacteria. The bacterial endotoxins test is described in USP chapter <85>. FDA guidance notes that <85> and two related documents describe the fundamental principles of the gel clot, photometric and kinetic test methods. The result is reported in endotoxin units (EU), a measure of endotoxin activity relative to a reference standard, usually per volume or per mass. A complete line names the method, the unit, the result and the limit the result was compared with. The same FDA guidance discusses interference from the sample itself, which can inhibit or enhance the reaction, so a lab should be able to say how it checked for that.

Metals. A metals line should say which elements were measured, by what method and against what limit. ICH Q3D(R2) places arsenic, cadmium, mercury and lead in Class 1, which it describes as human toxicants with limited or no use in pharmaceutical manufacturing. That guideline applies to drug products, so it is useful here only for showing which elements a metals line should name. A line that says “pass” with no elements, method or limit gives you little to check.

Sterility. A sterility test places samples in growth medium and watches for microbial growth over an incubation period. FDA guidance on aseptic processing notes that USP chapter <71> is the principal source for sterility testing methods and that sterility tests are limited in their ability to detect contamination because of the small sample size typically used. A pass therefore describes the units tested, not every vial.

How can I tell a COA is fake or reused?

No single sign proves a COA is false. Each of these is a reason to ask questions:

  • No lot number, or a lot number that differs from the vial’s.
  • No test date, or dates in the wrong order.
  • No lab name, address or contact, or a lab you cannot find independently.
  • No named methods, and no chromatogram or spectrum.
  • A stated purity that the chromatogram does not support, such as several clear peaks beside a figure of 99.9%.
  • Identical or repeated results on different lots, or the same report identifier on more than one lot.
  • An accreditation logo with no accreditation body, number or scope behind it.
  • Visible editing, such as mismatched fonts, uneven spacing or pasted-in values.

To verify a report, find the lab’s contact details yourself rather than from the document. Give the lab the report identifier and the lot number, and ask it to confirm that it issued a report with that identifier, for that lot, with those results. ISO/IEC 17025 expects each report to carry a unique identification and to identify the person who authorized it, so a lab that cannot find a report by its identifier has told you something.

Last reviewed: 2026-10-18

References

Frequently asked questions

What is a certificate of analysis for a research peptide?

A certificate of analysis (COA) is a lab's report of what it measured in one specific lot. It should name the lab, the lot, the dates, the methods and the results, and it applies only to the lot that was tested.

Does 99% purity mean 99% of the powder is peptide?

No. Purity usually means the main HPLC peak accounted for 99% of the detected signal. The detector does not see water, and salts and counterions may or may not be counted, so net peptide content is a separate question that a COA may or may not answer.

Does an ISO/IEC 17025 claim on a COA mean the product is certified?

No. ISO/IEC 17025 concerns the competence of a testing laboratory, not the product. Accreditation also covers a defined scope of tests, so check that the accreditation body's listing includes the tests on the report.

How can I confirm a COA is genuine?

Find the issuing lab's contact details yourself, not from the document. Give the lab the report identifier and the lot number, and ask it to confirm that it issued that report with those results.

Is a COA from the seller's own lab less reliable than one from an outside lab?

Not automatically. An outside lab separates the maker from the reporter, though the seller may still be the one paying for the test. Either way, look for the same fields, named methods, accreditation scope and a report identifier the lab can confirm.