When does carbon 14 dating become impractical
These considerations could therefore easily require an exposure to carbon 14 of 100,000 to 1,000,000 times the carbon 14 contained in the sample obtained for analysis.
The quantity required to be injected becomes even greater when shorter times for analysis (e.g., less than 5 minutes) are required due to short residence time in automated analytical equipment.
In accordance with the present invention, a carbon compound selected from the group consisting of elemental carbon, carbon monoxide (CO), carbon disulfide (CS ions are then produced and detected from the carbon compound at a known producing and detecting efficiency to provide a sufficient number of counts per minute by mass spectrometry of ions of the carbon isotope to be detected and quantified.
The detecting efficiency is a known characteristic of the detector employed and the producing efficiency is usually determined by simultaneously producing ions from a known quantity of an isotope other than the isotope to be quantified.
When a statistical precision of 1% or better is required, it would take over two hours to quantitatively determine less than 1×10 gram of carbon 14 becomes completely impractical by this method over any period of time due to the interference of background radiation.
The detection and quantification of carbon 14 in an amount even as low as 1×10 gram are quantities which are undesirably high to permit the use of carbon 14 as an in vivo biological radioactive tracer in humans.
The non-radioactive and more common (one trillionth) gram of carbon 14 cannot be quantitatively determined by scintillation counting in less than one hour with a statistical precision of 5% or better.This method requires extremely costly equipment and requires relatively large sample sizes. gram at a statistical precision of better than 5% within a time period of less than about 5 minutes.An attempt has been made to determine carbon 14 by converting carbon to CO by mass spectrometry (U. The method comprises producing a carbon compound selected from the group consisting of elemental carbon, CO, CS ions from the carbon compound at a known efficiency to provide at least 80 counts of carbon isotope ions per minute by mass spectrometry.Sufficient C ions of both isotopes are then produced and detected from the carbon compound to provide a sufficient number of counts of each carbon isotope by mass spectrometry to determine the ratio of the isotopes which is the same as the ratio of the number of counts.When the quantity of one of the isotopes is known prior to analysis by the method in accordance with the present invention, the quantity of the other isotope can, of course, be readily calculated from the quantity of known isotope.