You check a COA in two stages. First, check the document itself for consistency and signs of copying. Second, check that it belongs to the goods, by matching batch numbers and testing a sample that someone independent draws from the actual drums or tank.
A perfect-looking COA proves little on its own. Copying a good result onto a new batch is easy. Linking the paper to the goods is the real check.
Checking the document
- Confirm the company name, address and product name match the contract, SDS and invoice.
- Check the batch number format against previous COAs from the same plant.
- Check that the manufacturing, test and expiry dates are in a logical order and fit the production schedule you were given.
- Look for results identical to the decimal across several batches, which suggests copying rather than testing.
- Look for results sitting exactly on the limit, or every result being perfect, which is unusual for real data.
- Check that each test method is one the plant's lab can actually run. A small lab without a gas chromatograph cannot report a GC purity.
- Make sure the signature belongs to a named person in quality control, not the sales team.
Linking the COA to the goods
This is where most problems are caught. Do these at loading, not after arrival:
- Check that the batch number on the COA appears on every drum, bag or IBC label.
- Check the same batch number appears on the packing list and, where possible, on the invoice.
- Have an independent inspector draw samples from a set number of containers, following correct sampling practice.
- Seal the samples, keep one as a retention sample and send one to an independent lab.
- Compare the lab result with the COA on the key parameters.
Asking the plant directly
A genuine manufacturer can show you the raw data behind a COA: the chromatogram, the titration record or the lab notebook entry. Ask for it on the first order. A plant that cannot or will not show it is telling you something.
If the COA comes from a trader, ask for the original maker's COA as well. The two should match. Our general guide on reading a lab certificate covers independent lab reports.
Building a COA history
Keep every COA you receive from each supplier in one place, with your own test results beside them. Over a few lots you will see the plant's normal range for each parameter. A new COA that sits far outside that range, or that is suspiciously identical to an old one, stands out at once. The same history helps in a dispute, because it shows what the plant normally delivers and what it promised. It also helps you tighten your specification over time to match what good batches actually achieve.
Next step
We check COAs, supervise sampling at loading and have lots tested before shipment. Book a free sourcing review to set this up for your next order.