32.
In this study a field‐sampling technique for dissolved hydrogen (H
2) in groundwater will be presented which allows the transport of gaseous samples into the laboratory for further analysis. The method consists of transferring the headspace trapped in a gas‐sampling bulb which is continuously purged by groundwater into previously evacuated vials using a gas‐tight syringe. Three transfer steps with preceding evacuation of the vial led to a H
2‐recovery of 100 % in laboratory experiments. The method has been applied to determine H
2 concentrations in an aquifer contaminated with chlorinated solvents. Tests concerning the effect of different pumping techniques on H
2 concentrations revealed that most reliable values were obtained with a bladder pump, while an electrically driven submersible pump generated considerable amounts of hydrogen due to electrochemical interactions with the sampled water. Concentrations of dissolved hydrogen in field and laboratory samples were about two orders of magnitude higher when sampling was performed with the electrically driven submersible pump compared to sampling with the bladder pump and a peristaltic pump. Lab experiments with a Plexiglas reservoir to produce H
2‐enriched water were used to study the effect of two tubing materials (PVC, polyamide) on H
2 losses. PVC tubing turned out to allow transfer of H
2‐enriched water over 25 m without significant losses, while PA‐tubing was not suitable for sampling of H
2.
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