A sample must not be secondarily contaminated by younger or older carbon.

It is possible to remove some contaminants from a sample, such as root penetration into the sample, mould infestation, and more. It is appropriate to alert the laboratory about these facts through the entry form

Samples from old research stored in depositories can also be dated. However, preservatives carry a risk that can significantly affect the dating result. It is advisable to consult the analysis of such samples since some preservatives cannot be removed. Any information on sample preservation, such as protocol, reagent name, or at least the time of preservation, will be advantageous.