Chemical Quality · Guide

What Is a COA? How to Read a Certificate of Analysis

What a COA contains, how to read its parameters correctly, and how to tell whether one can be trusted.

When you buy chemicals, the label on the packaging tells you only the product name and a general purity. To know whether the specific lot you received really meets the quality you paid for, the document to check is the COA. Understanding and reading a COA correctly helps you avoid accepting substandard goods and gives you a clear basis for a claim when needed.

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What is a COA?

COA stands for Certificate of Analysis. It is a document issued by the manufacturer or a testing laboratory that records the actual test results of one specific lot and compares them with the committed specification. A COA answers one question: does this lot meet its specifications?

The key point is that a COA belongs to a specific production lot, not to the product in general. Two lots of the same product can give different results, so every lot must come with its own COA.

What does a COA usually contain?

Product information — chemical name, CAS number and grade.

Lot information — lot or batch number, manufacturing date, expiry or retest date.

Test parameters — the properties measured, such as purity, water content, color and density.

Specification — the permitted limit for each parameter, such as a minimum or maximum.

Actual result — the value measured for that lot.

Test method — how each parameter was measured, for example gas chromatography or Karl Fischer titration.

Conclusion — whether the lot passes or fails against the specification.

Authorization — the manufacturer's name and the signature or stamp of the quality-control department.

An example of reading a COA

The table below is an illustrative example for a generic solvent, meant to show the structure. The figures are for reference only and are not the official specification of any product.

Parameter	Specification	Result	Method
Purity	≥ 99.5 %	99.8 %	Gas chromatography (GC)
Water content	≤ 0.1 %	0.05 %	Karl Fischer
Color (Pt-Co)	≤ 10	5	Color comparison
Density (20 °C)	0.785 – 0.787 g/cm³	0.786 g/cm³	Density meter
Residue on evaporation	≤ 0.005 %	0.002 %	Gravimetric

Reading it is simple: for each row, compare the Result column with the Specification column. If the result is within the limit, it passes. In the example above, purity of 99.8 % is above the minimum of 99.5 %, and water content of 0.05 % is below the maximum of 0.1 %, so both pass.

Common parameters and what they mean

Parameter	What it tells you
Purity (assay)	The proportion of the main substance. The higher it is, the fewer the impurities
Water content	Affects reactions, stability and the final product, and is especially critical for battery grade
Color (APHA, Pt-Co)	A sign of contamination or degradation; the lower the number, the clearer the product
Density	A quick check of product consistency
Acidity or alkalinity	Residual acid or base, which affects corrosiveness and stability
Residue on evaporation	The non-volatile matter left behind, reflecting hard-to-evaporate impurities
Heavy metals	Important for food, cosmetics, pharmaceuticals and batteries
Microbiological parameters	Mainly applied to food grade

COAs differ by grade

Industrial grade — usually covers purity, water content, color and a few basic parameters.

Food grade — adds heavy metals, impurities under food standards and, depending on the product, microbiological parameters.

Battery grade — requires water content and metal impurities at very low levels, often measured in ppm.

USP, pharmaceutical and cosmetic grade — tight impurity control, and may include test methods from a pharmacopoeia.

So when ordering, state the grade you need and ask for a COA that includes the parameters of that grade.

How does a COA differ from an SDS and a TDS?

Document	Main content	Question it answers
COA	Analysis results for each lot	Does this lot meet the specifications?
SDS	Hazards, safety, storage, emergency response	How do I use this chemical safely?
TDS	Technical specifications and applications	What is this product for, and what are its properties?

The three documents complement each other. When buying, ask for all three. You can also read our article on SDS/MSDS on this website.

Warning signs of a questionable COA

No lot number — it cannot be matched to the actual goods.

Lot number differs from the packaging — the COA does not belong to the lot you received.

Results too round and too perfect — every parameter is flawless or identical across many lots.

No test method — results are listed without saying how they were measured.

No manufacturer information — the issuer's name, stamp or signature is missing.

Parameters do not fit the grade — for example food grade with no heavy-metal test.

Visible alteration — mismatched fonts, odd number placement or signs of editing.

How to check that a COA can be trusted

Match the lot number — the lot number on the COA must match the one printed on the packaging or delivery note.

Send a sample for independent testing — for large-value lots or new products, send a sample to a third-party laboratory.

Compare between lots — COAs for consecutive shipments should be stable, without unusual swings.

Keep a retained sample of each lot — so you have a basis for claims or traceability.

Write commitments into the contract — minimum specifications and how off-spec goods will be handled.

Common mistakes with COAs

Looking only at purity — ignoring water content, color or heavy metals, which can decide the final product quality.

Using the COA of another lot — an old COA does not reflect the quality of a new lot.

Receiving a COA but not checking it — no lot matching and no retained sample.

Not stating required parameters when ordering — the supplier sends a COA based on its own internal standard, missing the parameters you need.

Frequently asked questions

Is a COA mandatory?

Not always required by law, but it is almost a standard commercial requirement. For food, batteries or exports it is especially important.

How does a COA differ from a quality certificate?

A COA is the test result of one specific lot. Certificates such as ISO, HALAL or Kosher certify a system or process and do not replace a COA.

Can I request a COA before ordering?

Yes. Ask for a sample COA to see the structure and parameters, and for a separate COA for each lot at delivery.

What if the actual result differs from the COA?

Keep the sample and packaging, take photos, match the lot number and notify the supplier immediately under the contract terms.

How do I get a COA from CHEINGAR-CHEM?

Send us the product name, grade and quantity. We will provide the COA and matching technical documents on request.

Need a COA or advice on chemical quality?

Contact CHEINGAR-CHEM CO., LTD for technical documents, a quotation and a sample for each product.

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What Is a COA? How to Read a Certificate of Analysis

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