How to Read a Certificate of Analysis (COA) for Chemicals

A certificate of analysis (COA) is the quality report for one specific production lot. It tells you what was tested, the limits the lot had to meet and the actual results. Reading it properly takes two minutes and can save a rejected batch.

What a COA should include

• Product name, grade and CAS number
• Batch / lot number, plus manufacturing and expiry or retest date
• Test parameters, the specification limit for each and the actual result
• Test methods used (for example IS, ASTM, or the BP / USP monograph for pharma grades)
• Signature of the authorised quality-control person and the issuing lab

How to check it

1. Match the lot number on the COA with the lot printed on the bags, drums or labels you received.
2. Compare against your own specification, not just the supplier's limits — they are not always the same.
3. Focus on the parameters that matter for your process. For example: iron content in caustic soda used in textiles or water treatment, moisture in hygroscopic powders, or heavy metals in food and pharma grades.
4. Check the dates. Some products have a retest date after which results must be confirmed again.
5. For critical uses, test a retained sample in an independent lab, at least for the first few lots from a new supplier.

Example: caustic soda flakes

Parameter	Typical limit	What it tells you
Assay (as NaOH)	Min. 98.0%	Strength of the product
Sodium carbonate (Na₂CO₃)	Max. 0.5%	Exposure to air during production or storage
Sodium chloride (NaCl)	Max. 0.1%	Purity of the process
Iron (Fe)	Max. 20 ppm	Important for textile and water-treatment use

Limits vary by grade and standard — always agree the specification before ordering.

Red flags

• A generic "typical analysis" sheet with no lot number
• Every result exactly equal to the limit
• No test methods, no signature or no lab details
• A COA dated long before the goods were packed

Need a COA for one of our products? See Caustic Soda Flakes or contact us — we share a COA with every lot.