C-14 analysis of groundwater down to the millilitre level

Two new methods for the sample preparation of groundwater for C-14 measurements with accelerator mass spectrometry (AMS) were developed and tested. Both methods are simple and do not require vacuum for the extraction of CO2 from water. A double needle with flow controlled He carrier gas is used for air flushing out before the reaction and also for the CO2 transfer out from the septa sealed reactor test tube. The extracted CO2 was either graphitized or directly measured with an AMS equipped with a gas ion source. The processing blank and the reproducibility of the applied methods are satisfactory and allow precise groundwater C-14 analyses. The feasibility of field sampling directly into the reaction tubes was demonstrated using very old (1-20 pMC) groundwater samples. The C-14 content of as little as 1 mL of water sample could be measured with 1% precision (for a modern sample) within 20 min with the gas ion source of a MICADAS type AMS system. The preparation of the samples can be performed while measurements are already running and therefore require no additional time. (C) 2012 Elsevier B.V. All rights reserved.