A mass spectrometric line for tritium analysis of water and noble gas measurements from different water amounts in the range of microlitres and millilitres

Abstract

This paper describes the procedure followed for noble gas measurements for litres, millilitres and microlitres of water samples in our laboratory, including sample preparation, mass spectrometric measurement procedure, and the complete calibrations. The preparation line extracts dissolved gases from water samples of volumes of 0.2 μ l to 3 l and it separates them as noble and other chemically active gases. Our compact system handles the following measurements: (i) determination of tritium concentration of environmental water samples by the ³He ingrowth method; (ii) noble gas measurements from surface water and groundwater; and (iii) noble gas measurements from fluid inclusions of solid geological archives (e.g. speleothems). As a result, the tritium measurements have a detection limit of 0.012 TU, and the expectation value (between 1 and 20 TU) is within 0.2 % of the real concentrations with a standard deviation of 2.4 %. The reproducibility of noble gas measurements for water samples of 20–40 ml allows us to determine solubility temperatures by an uncertainty better than 0.5 °C. Moreover, noble gas measurements for tiny water amounts (in the microlitre range) show that the results of the performed calibration measurements for most noble gas isotopes occur with a deviation of less than 2 %. Theoretically, these precisions for noble gas concentrations obtained from measurements of waters samples of a few microlitres allow us to determine noble gas temperatures by an uncertainty of less than 1 °C. Here, we present the first noble gas measurements of tiny amounts of artificial water samples prepared under laboratory conditions.

Keywords:

• age dating
• helium-3
• helium-4
• isotope measurements
• methods and equipment
• noble gas mass spectrometry
• palaeoclimate reconstruction
• tritium
• water

Acknowledgements

This work was party supported by the Marie Curie Reintegration Grant (No. 221946). We thank the reviewers for their helpful comments.

Notes

^†Presentation at the 11th Isotope Workshop of the European Society for Isotope Research (ESIR), Budapest, July 4–8, 2011.