Abstract
Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is being routinely used to quantify trace impurities in bulk gases used in the manufacture of semiconductor devices. APCI-MS has been successfully applied for the quantification of ppt (ng/Kg) levels of O2, H2O, CO2 and CH4 in Ar, N2 and He and trace N2 in He. However it has not been successfully used to quantify ppt levels of N2 in Ar due to unfavorable rate constant for the charge transfer reaction between Ar+ and N2. We report here the detection of ppt levels of N2 in Ar by adding a few percent of purified H2 into the ionization source of the mass spectrometer. The addition of H2 results in a plasma dominated by protonated ions and the detection of trace N2 is facilitated by favorable proton transfer reactions to produce N2H+. Our experimental results indicate statistical detection limits below 50 ppt.
Published Version
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