Chain of custody
CoCChain of custody is the documented record of who handled a sample, when, and under what conditions from the moment it was collected until testing was complete.
Each transfer is logged and signed, containers are sealed and labeled, and storage conditions are recorded, so that a result can be tied to a specific sample with confidence. The practice originated in forensic and drug testing, where it must withstand legal challenge, and it is a requirement of accredited laboratory operation. Gaps in the record undermine the result regardless of the quality of the analysis.
For product testing, chain of custody is what links a certificate of analysis to a particular batch: it documents that the sample tested came from that lot and was not substituted or altered along the way. Consumers rarely see the record itself, but its existence is implied whenever a certificate names a batch and a sample identifier. In workplace drug testing, the same concept governs the urine sample, and a break in the chain can invalidate the test.