Collagen is sometimes degraded, in which case it may be necessary to separate the proteins into individual amino acids and measure their respective ratios and 14C activity.
It is possible to detect if there has been any degradation of the sample by comparing the relative volume of each amino acid with the known profile for bone.
[2] Shells from both marine and land organisms consist almost entirely of calcium carbonate, either as aragonite or as calcite, or some mixture of the two.
The process takes about a month, and requires a sample about ten times as large as would be needed otherwise, but it allows more precise measurement of the 14C/12C ratio in old material, and extends the maximum age that can be reliably reported.
Libby's first measurements were made with lamp black,[7] but this technique is no longer in use; these methods were susceptible to problems caused by the 14C created by nuclear testing in the 1950s and 1960s.
The resulting gas was passed through hot copper oxide to convert any carbon monoxide to CO2, and then dried to remove any water vapour.
[11] To prepare benzene for liquid scintillation counting, the sequence begins with combustion to convert the carbon in the sample to CO2.
[7] Targets for accelerator mass spectrometry are prepared from CO2 by catalysing the reduction of the gas in the presence of hydrogen.
This results in a coating of filamentous carbon (usually referred to as graphite) on the powdered catalyst—typically cobalt or iron.
A rough guide follows; the weights given, in grams, are for dry samples, and assume that a visual inspection has been done to remove foreign objects.