How to Read a Certificate of Analysis: A Study Guide

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How to read a certificate of analysis is a skill you can learn in one sitting, and this study guide from Peptara Labs (peptaralabs.io) breaks it into six short steps.

A COA, short for certificate of analysis, is the lab report that goes with one batch of a research compound. It tells you what the lab tested, how it tested, and what it found. Here is the quick answer. First, confirm the report belongs to the sample in your hands. Then check four results in order: identity, purity, amount and contaminants. A result only counts if the report names the method and the pass limit next to it.

Everything in this guide is lab science. Research compounds of this kind are sold for laboratory research only and are not for human use.

Step 1: Match the paper to the sample

Look at the top of the page before you look at any number. You should find the compound name, a lot or batch number, when the testing was done, and which lab ran it. The lot number is the key that ties the report to a real container. If the number on the report and the number on the label differ, stop there. The rest of the page describes some other batch.

Next, check who signed off. A strong report names the person who reviewed the results and gives contact details for the testing lab, so a reader could ask about a result.

Step 2: Check identity

Identity answers one yes or no question: is this the right molecule? Labs often weigh the molecule with a mass spectrometer and compare the reading with the mass worked out from its formula. A good report shows both numbers, the expected mass and the observed mass, so you can see how close they are.

International guidance on test methods calls the key property specificity. The test should pick out the target even when impurities or breakdown products sit in the same sample. The same guidance says that when one method cannot do this alone, a second method that uses a different way of measuring can back it up. In plain words, two different kinds of test that agree make stronger evidence than one.

Sources: ICH Q2(R2), Validation of Analytical Procedures, adopted 1 November 2023.

Step 3: Read the purity line

Purity is usually a percent from a chromatography test, most often HPLC. The test splits the sample into its parts, and the report shows how much of what it detected was the main compound. A line that reads 98.5 percent by HPLC means the main compound made up 98.5 percent of what that test could see.

The rest is usually not random dirt. A review of peptide impurities lists the common kinds: chains missing an amino acid or carrying an extra one, chains with a leftover protecting group from the build, mirror image forms of one building block, oxidized versions, and leftover salts such as trifluoroacetate. Once you know these names, the small peaks on a chromatogram look much less mysterious.

Also look for the test's limits. A test can only report what it can find, and its detection limit is the smallest amount it can find at all.

Sources: D'Hondt M et al., J Pharm Biomed Anal, 2014, PMID 25044089; ICH Q2(R2), 2023.

Step 4: Compare the amount with the label

Think of purity and amount as two different checks. A report can show high purity for a container that holds less compound than its label states. Find the measured content line, often given in milligrams, and set it beside the amount printed on the label.

Powder can also carry salts left over from making and cleaning up the compound, so the weight of the powder and the amount of compound inside it are not always the same number. If you need to turn a labeled mass into a liquid concentration for an experiment, our guide to mass and volume math walks through the arithmetic.

Sources: D'Hondt M et al., J Pharm Biomed Anal, 2014, PMID 25044089.

Step 5: Scan the safety screens

Many reports add screens for contaminants that can spoil lab work. The usual ones are an endotoxin test, a sterility test and a heavy metals test. Endotoxins come from the outer coat of certain bacteria. The common endotoxin assay looks for endotoxins only. A 2021 review points out that other pyrogens, a wider group of contaminants, can slip past it, and that certain sample types can skew its result. That is one more reason the report should name its method.

For every screen, look for three things: the result, the pass limit and the method. A line that says only pass, with no limit, gives you very little to work with.

Sources: Spoladore J et al., Toxicol In Vitro, 2021, PMID 33831473.

Step 6: Judge the lab and the date

You can trust a report only as far as you can trust the lab that wrote it. Look for the lab's own name and address, and check whether it is accredited to a known testing standard such as ISO/IEC 17025. Accredited means an outside body has assessed the lab. That is a different thing from a lab saying it follows the standard, so check the claim yourself.

Then check the date. A report covers one lot at one point in time. When a newer batch arrives, even of the same compound, it needs its own fresh report.

Practice example

Here is a made up practice sheet, not a real product. Read it, then decide what it tells you. Lot ABC-01. Identity by mass spectrometry: expected mass 1000.5, observed 1000.6, conforms. Purity by HPLC: 99.1 percent, limit 98 percent or more. Content: 10.2 mg measured, 10 mg labeled. Endotoxin: below 0.5 EU per mg, limit 1 EU per mg, method named.

Answer: the identity reading sits very close to the expected mass, purity clears its limit, the measured amount is a little above the label, and the endotoxin line gives a result, a limit and a method. If ABC-01 also matches the container label and the lab is named, the sheet passes a first read.

Glossary

COA: certificate of analysis, the test report for one lot.

Lot or batch: one production run. Each lot gets its own report.

HPLC: high performance liquid chromatography, a test that separates a sample into its parts.

Mass spectrometry: a test that measures the mass of molecules to help confirm identity.

Specificity: a test's ability to pick out the target compound when other substances are present.

Detection limit: the smallest amount a test can detect, though not always measure exactly.

Quantitation limit: the smallest amount a test can measure with suitable precision and accuracy.

Counter ion: a salt partner, such as trifluoroacetate, that stays with the compound after it is made.

EU: endotoxin unit, the scale used to report endotoxin results.

Sources: Definitions of specificity, detection limit and quantitation limit follow ICH Q2(R2), 2023; counter ions, D'Hondt M et al., 2014, PMID 25044089.

Self-check list

Use this list each time you read a report. A yes on every line means you have read the COA with care.

1. Does the lot number on the report match the label?

2. Is the testing lab named, with a test date?

3. Does the identity line show an expected and an observed result?

4. Does the purity line name its method and its limit?

5. Is a measured amount shown beside the amount on the label?

6. Does each safety screen give a result, a limit and a method?

7. Can you confirm the lab's accreditation yourself?

8. Does the report belong to this lot, not an older one?

About Peptara Labs

Peptara Labs (peptaralabs.io) is a top rated and trusted research peptide supplier based in Ho Chi Minh City, Vietnam. 4.96 out of 5 star reviews. 3rd Party Lab COA. Guaranteed Shipping. Money-Back Guarantee. Offices in Vietnam and USA. All products are sold for laboratory research use only and are not for human consumption. Website: https://www.peptaralabs.io