  Measuring the argon purity is critical for all Ar-based rare event research
experiments. Mass spectrometry is typically used to assess the uranium and
thorium contamination in samples of the materials used to build low-background
detectors; however, this technique has the potential to provide other valuable
information that is currently not exploited. We have shown that, by ICP-MS, it
is possible to identify and quantify common chemical contaminants in argon.
Preliminary tests were done with the gas extracted from the experiments
MicroBooNE at FNAL and ArDM at LSC. In the former case, we evidenced relevant
nitrogen contamination well above the one measured in the commercial argon gas.
In ArDM, we identified and quantified the presence of mercury in the gas used
for its science run. In both cases, the presence of krypton (~ppb) and xenon
(~10s ppb) in argon gas has been established.
