Chain of custody designates the complete documentation of all pre-analytical and analytical steps in analysis of a sample. This includes all procedures starting from the identification of the person to be tested with identity card, the sample collection, the transport of the sample to the laboratory, the technical analysis of the sample and finally the issuing of a report or a written expert testimony.
All steps are exactly documented so that at a later date it can be traced who, how, where and when the sample was processed.
The results of the analysis are kept together with the sample and stored as long as recommended in the corresponding guidelines.
This approach is particularly important in forensic toxicology in case the person tested or the requesting authority later on (possible in judicial proceedings) has questions related to the analytical procedures or challenges the result of the analysis.