Review of water DIC-14 analyses at HEKAL via a case study: sampling-storage-preparation

Anita Molnár1, Róbert Janovics2, László Palcsu2, Virág Gergely2, István Futó2, Mihály Veres1, Péter Molnár3, János Országh3, Mihály Molnár2

1Isotoptech Zrt, Debrecen, Hungary, 2INTERACT Centre, Institute for Nuclear Research , Debrecen, Hungary, 3Public Limited Company for Radioactive Waste Management (PURAM), Pécs, Hungary

Keywords: water, DIC, radiocarbon, storage, preparation

The aim of this study was to investigate the overall performance, stability and reliability of the applied water sampling, sample storage and preparation protocols for dissolved inorganic carbon (DIC) C-14 AMS analyses at HEKAL AMS Facility (Debrecen, Hungary). For this purpose we have selected a study site in Southern Hungary (Mecsek Mountains), where deep groundwater monitoring wells are operated routinely. Several different sampling methods, sample conservation techniques and storage conditions have been investigated on real groundwater samples. Some of the wells had rather old (<2 pMC) DIC and some of them had moderate C-14 age (10-20 pMC).
We have investigated the effect of adding sodium-iodine (KI) based conservation, the type/quality of the sampling bottles and their cups and different storage conditions. In the course of the test sampling/analyses, multiple parallel DIC samples were collected from 5 different monitoring wells. Some of the samples have got KI addition as a conservation step, others did not got any added chemicals during sample collection. Conservated and pure DIC samples were stored in refrigerator (at 12 C degree) between the sampling time and sample preparation for C-14 analyses, while a control group of the same samples were stored at room temperature. We have tested the stability of the samples by repeated DIC-14 analyses after 2 weeks and more than 1 month storage, for all type of samples. Some bottles have been opened twice, for the 1st and 2nd analyses, while others were kept closed for more than 1 month. Repeated DIC sampling and preparation from the same wells showed the internal reproducibility of the applied methods. Accidental leaking of the bottle cups were also studied, as a possible source of random error during sample storage. In this study we analyse all the observed effect and they potential on influencing the final DIC-14 results.
The research was supported by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.4-15-2020-00007 “INTERACT”. Prepared with the professional support of the Doctoral Student Scholarship program of the co-operative doctoral program of the Ministry of Innovation and Technology financed from the National Research, Development and Innovation found. This work was carried out in the frame of a János Bolyai Research Scholarship (to Mihály Molnár) of the Hungarian Academy of Sciences.


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Date

Nov 08 - 19 2021