A High-Throughput Method for the Conversion of CO₂ Obtained from Biochemical Samples to Graphite in Septa-Sealed Vials for Quantification of ¹⁴C via Accelerator Mass Spectrometry

Abstract

The growth of accelerator mass spectrometry as a tool for quantitative isotope ratio analysis in the biosciences necessitates high-throughput sample preparation. A method has been developed to convert CO(2) obtained from carbonaceous samples to solid graphite for highly sensitive and precise (14)C quantification. Septa-sealed vials are used along with commercially available disposable materials, eliminating sample cross contamination, minimizing complex handling, and keeping per sample costs low. Samples containing between 0.25 and 10 mg of total carbon can be reduced to graphite in approximately 4 h in routine operation. Approximately 150 samples per 8-h day can be prepared by a single technician.

Accelerator mass spectrometry of small biological samples

“…Secondly, it should be noted that the gradients of the two sets of data are similar, indicating that the two sample preparation methods give similar results. Method 1 indicates a higher offset, indicating a higher level of 12 C contamination. The latter also has a characteristically higher stochastic scatter.…”

“…For routine, high-throughput sample production, we use the method of Ognibene et al, 12 which has been modified for the preparation of small samples 3 and will only be briefly described here. The samples are placed in quartz tubes with CuO powder ($100 mg), dried, evacuated to about 5 Á 10 À4 mbar and vacuum-sealed.…”

“…The vacuum throughout the system is in the order of 3 Á 10 À8 mbar. Isotopic ratios are then measured by single particle counting of 14 C in a solid-state detector and current measurements of 13,12 C in a Faraday cup. The 14 C/ 12 C ratio, R, is presented in units of Modern (M) or as a percentage of Modern (pMC).…”

“…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.…”

“…This increased isotopic ratio has been transcribed in the DNA molecules of living organisms as a result of the ecological cycle. As the DNA molecule is stable and the chronological profile of the 14 C to 12 C ratio in living matter is well documented, one can use the AMS isotopic ratio measurement to date the DNA molecules. The method has also been applied in forensic science to determine the ages of the 2004 South East Asia Tsunami victims by performing AMS analysis of the teeth.…”