Any organic material that is available in sufficient quantity can be prepared for radiocarbon dating.
Modern AMS (accelerator mass spectroscopy) methods require tiny amounts, about 50 mg.
During the lifetime of an organism, the amount of c14 in the tissues remains at an equilibrium since the loss (through radioactive decay) is balanced by the gain (through uptake via photosynthesis or consumption of organically fixed carbon).
However, when the organism dies, the amount of c14 declines such that the longer the time since death the lower the levels of c14 in organic tissue.
Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.
Plants take up c14 along with other carbon isotopes during photosynthesis in the proportions that occur in the atmosphere; animals acquire c14 by eating the plants (or other animals).Bases may be used to remove contaminating humic acids.Some types of samples require more extensive pre-treatment than others, and these methods have evolved over the first 50 years of radiocarbon dating.The sample must be destroyed in order to measure its c14 content.The first measurements of radiocarbon were made in screen-walled Geiger counters with the sample prepared for measurement in a solid form.