Age dating contamination
Thus, even if larger samples like RATE’s “on the order of 100 mg”  are submitted to an AMS laboratory, only about 1 mg of carbon will actually undergo analysis.Though Baumgardner calls a 1 mg sample “tiny” , it is generally considered “large” by AMS laboratories [e.g., 5, 7, 8], with enough carbon to provide ion source current for about a day.But the amount of contamination is generally impossible to quantify.An old sample with in situ contamination cannot generally provide an accurate date.Furthermore, the instrument itself always introduces a background, similar to most other high sensitivity analytical instruments .A sample originally containing absolutely no radiocarbon will still give a nonzero measurement from such contributions.John Baumgardner, a geophysicist with expertise in tectonic modeling, presents experimental data claiming to show that all biological material contains intrinsic radiocarbon, no matter how old that material may be thought to be [1, 2].
In both cases, I am convinced that the “intrinsic radiocarbon” is nothing more than contamination and instrument background.
The maximum allowed sample size is typically about 10 mg of carbon.
Larger samples produce excessive CO pressure in the sealed tubes used in the process, causing tubes to explode and samples to be lost.
Most laboratories prefer to receive samples larger than 1 mg to allow some loss in cleaning and to have additional material available if needed.
Modern radiocarbon dating by AMS is a complex process with numerous potential sources of contamination requiring characterization.
The age limit was roughly 30k years, due both to poor statistics from low decay count rates and to cosmic ray backgrounds.