How to read a Certificate of Analysis

What a Certificate of Analysis is

A Certificate of Analysis, or CoA, is a lab report for one specific batch of a product. It lists the tests that were run, the result of each test, and the limit the result had to meet.

In real drug manufacturing, the rules are strict. The international manufacturing guide that FDA uses for drug ingredients says an authentic CoA should be issued for each batch. It should name the product and the batch number, list every test with its limit and its actual number, be signed and dated by the quality team, and give the name and address of the original maker.^[1]

A CoA posted by an online peptide seller is a different thing. Nobody at FDA reviews it. It is only as good as the lab that made it and the honesty of the person who posted it.

What HPLC purity shows, and what it does not

HPLC stands for high performance liquid chromatography. The lab dissolves a small sample and pushes it through a packed tube. Different molecules come out at different times, and a detector draws each one as a peak on a graph called a chromatogram. The purity number is usually the size of the main peak as a percent of all the peaks the detector saw.^[2]

That number has real limits:

• It only counts what the detector sees. Water, leftover solvents, salts and counter ions (small charged molecules stuck to the peptide) do not show up as peaks. They have to be measured with other tests.^[2]
• It is not the amount of peptide in the vial. A sample can be 99 percent pure by HPLC and still be partly water and salt by weight. Measuring the actual amount is a separate test.^[2]
• A peak alone does not prove identity. A peak at the right spot means more when the lab compares it with a known reference sample run the same way.^[2]
• Some problems hide. Mirror image versions of an amino acid, or two amino acids with the same weight, may need extra tests to tell apart.^[2]

What mass spectrometry shows, and what it does not

Mass spectrometry, often shortened to MS, weighs molecules. If the measured mass matches the expected molecular weight of the peptide, that is good evidence the main ingredient is the right molecule. A more detailed version can also confirm the order of the amino acids.^[2]

MS does not tell you how much peptide is in the vial or how pure it is. It can also miss a swap between two building blocks that weigh the same.^[2] For generic peptide drugs, FDA encourages makers to use several different methods, including sensitive high resolution tests, because small impurities such as an extra or missing amino acid could cause immune reactions.^[3]

What to look for on a CoA

• A real lab name and contact details. You should be able to find the lab and reach it.^[1]
• A batch or lot number that matches your vial. A CoA for a different batch tells you nothing about yours.^[1]
• A test date. The test should come before the batch was sold, and it should not be years old.
• The product name and its expected molecular weight. Compare the expected weight with the compound page in our library or with PubChem.
• The test methods. The report should say which methods were used, such as HPLC for purity and MS for identity.^[2]
• The actual chromatogram. Look for a picture of the peaks, with the time each peak appeared and a table of peak sizes.^[2]
• A measured mass that matches the expected weight. Look for a measured number from the instrument, not just the textbook value typed in.^[2]
• Limits and a pass or fail for each test, plus a signature and date from a named person.^[1]

Signs a CoA may be faked or reused

• The same CoA appears for every batch, or the date is very old.
• There is no batch number, or it does not match the vial.
• There is no chromatogram, or the image is blurry, cropped or looks edited.
• Every product shows the same near perfect number, such as 99.9 percent.
• The mass result is just the textbook molecular weight with no measured data.
• You cannot find the lab, or the lab will not confirm the report number when you contact it.

Real reviews show these gaps are common. When FDA looked at CoAs submitted for BPC-157, most reported only a purity number. The impurities were not identified, endotoxin testing was not mentioned, and the substance named did not always match the CoA.^[4] In a study that bought semaglutide vials from online sellers, the paperwork claimed purity of at least 99 percent. Lab testing measured purity of only about 8 to 14 percent.^[5]

Why third party testing matters

A seller testing its own product has an obvious conflict of interest. Even in regulated supply chains, when a broker or repacker issues a new certificate, it should name the lab that did the testing, name the original maker, and attach the original batch certificate.^[1]

Third party testing adds independence, but it has a limit. The lab can only vouch for the sample it received. If the seller picked and mailed that sample, it may not match what customers get. Testing of samples the lab bought on its own, like the study above, tells you more.^[5]

What a CoA usually does not cover

Most seller CoAs cover purity and identity only. Unless the CoA says so in writing, assume these were not tested:

• Sterility. This means no living germs. For injectable drugs, international standards list sterility as its own required test, separate from purity.^[6]
• Endotoxins. These are fever causing pieces of bacteria that can remain even after the bacteria are dead. Injectable drugs need their own endotoxin test, and FDA has detailed guidance on how to run it.^[6][7] In the online semaglutide study, endotoxin was measurable in every vial tested.^[5]
• Content. This is how many milligrams of actual peptide are in the vial. It is a separate test from purity.^[6] Counter ions alone can make up a large share of a peptide powder's weight. One study measured up to 35 percent.^[8]

Bottom line

A clean, matching, verifiable CoA is a minimum, not a guarantee. It covers one sample from one batch and usually only two tests. It does not make a product approved, legal or safe for people.

Sources

1. U.S. Food and Drug Administration. Q7 Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients, Guidance for Industry (Revision 1). September 2016. FDA guidance (PDF)
2. McCarthy D, Han Y, Carrick K, et al. Reference Standards to Support Quality of Synthetic Peptide Therapeutics. Pharm Res. 2023;40:1317-1328. doi:10.1007/s11095-023-03493-1
3. U.S. Food and Drug Administration. ANDAs for Certain Highly Purified Synthetic Peptide Drug Products That Refer to Listed Drugs of rDNA Origin, Draft Guidance for Industry. October 2017. FDA guidance (PDF)
4. U.S. Food and Drug Administration. FDA Evaluation of BPC-157 Related Bulk Drug Substances. Briefing document, Pharmacy Compounding Advisory Committee meeting, July 23-24, 2026. FDA briefing document (PDF)
5. Ashraf AR, Mackey TK, Vida RG, et al. Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. J Med Internet Res. 2024;26:e65440. doi:10.2196/65440
6. U.S. Food and Drug Administration. Q6A Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical Substances. December 2000. FDA guidance page
7. U.S. Food and Drug Administration. Pyrogen and Endotoxins Testing: Questions and Answers, Guidance for Industry. March 2026. FDA guidance page
8. Erckes V, Streuli A, Chamera Rendueles L, Krämer SD, Steuer C. Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides and Its Influence on Membrane Permeation. Pharmaceuticals. 2025;18(8):1163. doi:10.3390/ph18081163