Discussion Reporting of ¹⁴C Data

Abstract

Count rates, representing the rate of 14C decay, are the basic data obtained in a 14C laboratory. The conversion of this information into an age or geochemical parameters appears a simple matter at first. However, the path between counting and suitable 14C data reporting (table 1) causes headaches to many. Minor deflections in pathway, depending on personal interpretations, are possible and give end results that are not always useful for inter-laboratory comparisons. This discussion is an attempt to identify some of these problems and to recommend certain procedures by which reporting ambiguities can be avoided.

Accelerator mass spectrometry of small biological samples

“…The HPLC fractions typically have very small amounts of the labeled drug: in the pg to fg range. The specific activities of the drugs are, however, very high, usually in the tens of Ci/mol; this translates into the 10 9 Modern range, or equivalent to almost every drug molecule having a 14 C atom (1 Modern corresponds to present day 14 C content which is approximately 98 attomole 14 C/mg 12 C). The carbon-carrier method therefore facilitates accurate isotopic dilution which allows mass determination of the HPLC fraction.…”

“…The carbon-14 content varies significantly depending on the vendor, by as much as a factor of 50. We have used TRB from MP Biomedicals Inc. (Solon, OH, USA) which had the lowest 14 C content (<500 zmol of 14 C per mg 12 C). We have used typically 1.5 mg of TRB corresponding to about of 1 mg of carbon per sample.…”

“…Another unique aspect of AMS is the capability of detecting the isotopes, utilizing different methods. For example, 14 C is detected with a single particle detector, whereas 12 C is measured using a current detector achieving routine isotopic ratio determination in the 1:10 15 range. In an AMS setup, the whole accelerator is used as a mass spectrometer.…”

“…Some biological applications of AMS involve the measurement of 14 C-labeled organic compounds. The use of AMS for biological studies has been pioneered by Vogel et al at the Lawrence Livermore National Laboratory, LLNL.…”

“…The principle used is based on the release of large amounts of carbon-14 in the atmosphere during the 1950s and 1960s as a result of the nuclear bomb tests which nearly doubled the 14 C to 12 C isotopic ratio. This increased isotopic ratio has been transcribed in the DNA molecules of living organisms as a result of the ecological cycle.…”