A retention sample, also called a retained or reference sample, is a sealed portion of the lot you bought, kept unopened so it can be tested later. It is your evidence of what was shipped if a quality problem appears months after delivery.
Keep it at least until the product's shelf life has ended and your contract's claim period has passed, whichever is later. Many buyers add a margin on top, especially for products used slowly.
Why it matters
Quality problems often show up late. A dye may give a wrong shade only when your customer runs it on their machine. An intermediate may cause a yield loss in your process weeks after delivery. Without a sealed sample, it becomes your word against the supplier's.
A properly sealed retention sample lets an independent lab test the lot as it left the factory. If the sample fails, the supplier has a problem. If it passes, the cause may lie in transport, storage or use.
How it should be taken and kept
- Draw it at the same time as the pre-shipment sample, from the same randomly chosen packages, as described in drawing a chemical sample correctly.
- Seal it with a numbered seal in front of both sides, or an independent inspector.
- Label it with product, batch, date, seal number and the packages it came from.
- Store it in conditions that match the SDS and the product's storage advice, away from heat, light and moisture where relevant.
- Keep enough quantity to repeat the full set of tests at least twice, since a dispute often needs both a check test and an umpire test.
- Keep a log of where each sample is stored and who can open it, so it can be found quickly when a claim arises.
Who keeps which sample
The usual practice is a three-way split. One sealed set goes to you, one stays with the supplier, and one is held by an independent inspector or lab. Each party can then test or produce its sample if there is a claim. Your contract should say which sample decides the outcome if results differ.
Write the retention period into the contract as well. If the contract says nothing, the supplier may discard its own sample after a few months.
Setting the period
Start from the shelf life on the technical data sheet. Add the time you expect the lot to sit in your warehouse and your customer's. Then check the claim period in your contract and any time limits in your insurance policy. The longest of these sets your minimum. Your contract terms are covered in what a chemical purchase contract should include.
Next step
We draw and seal retention samples at loading and keep the records that make them usable in a claim. To start, book a free sourcing review.