[해외논문]The use of proton-transfer reactions to detect low levels of impurities in bulk oxygen using an atmospheric pressure ionization mass spectrometer
Ketkar, S.N.
(Air Products and Chemicals, 7201 Hamilton Boulevard, Allentown, PA 18195, USA)
,
Scott Jr., A.D.
(Air Products and Chemicals, 7201 Hamilton Boulevard, Allentown, PA 18195, USA)
,
Hunter Jr., E.J.
(Air Products and Chemicals, 7201 Hamilton Boulevard, Allentown, PA 18195, USA)
AbstractAtmospheric pressure ionization mass spectrometry (APIMS) is being routinely used to quantify trace impurities in bulk gases used in the manufacture of semiconductor devices. APIMS has been successfully applied for the quantification of ppt levels of O2, H2O, CO2, and CH4 in Ar, N2, and He. ...
AbstractAtmospheric pressure ionization mass spectrometry (APIMS) is being routinely used to quantify trace impurities in bulk gases used in the manufacture of semiconductor devices. APIMS has been successfully applied for the quantification of ppt levels of O2, H2O, CO2, and CH4 in Ar, N2, and He. However, it has not been successfully used to quantify trace impurities in bulk O2 because of the low ionization potential of O2. APIMS relies on charge-transfer reaction between the ions of the bulk gas molecules and impurity molecules. As all the relevant impurity molecules have ionization potentials higher than that of O2, APIMS has not been used to analyze for impurities in O2. A recent publication describes the use of a clustering reaction, as opposed to a charge-transfer reaction, to detect trace levels of H2O in bulk O2. Clustering reactions have not been successfully used to detect CO2, N2, and CH4 in bulk O2 because the relevant cluster ions are very weak and are declustered in the low-pressure declustering region normally used in an APIMS. O2 has a relatively low proton affinity, and protonated oxygen is expected to undergo proton transfer reactions with CO2, N2, and CH4. We report the use of H2, as a doping gas, in the source of an APIMS to facilitate the protonation of trace impurities in O2. For safety considerations, a buffer gas like He or Ar has to be added to keep the concentration of H2 below the lower explosion limit (LEL). Our results indicate a statistical limit of detection of 0.5 ppb for CH4, 0.3 ppb for CO2, and 1.2 ppb for N2.
AbstractAtmospheric pressure ionization mass spectrometry (APIMS) is being routinely used to quantify trace impurities in bulk gases used in the manufacture of semiconductor devices. APIMS has been successfully applied for the quantification of ppt levels of O2, H2O, CO2, and CH4 in Ar, N2, and He. However, it has not been successfully used to quantify trace impurities in bulk O2 because of the low ionization potential of O2. APIMS relies on charge-transfer reaction between the ions of the bulk gas molecules and impurity molecules. As all the relevant impurity molecules have ionization potentials higher than that of O2, APIMS has not been used to analyze for impurities in O2. A recent publication describes the use of a clustering reaction, as opposed to a charge-transfer reaction, to detect trace levels of H2O in bulk O2. Clustering reactions have not been successfully used to detect CO2, N2, and CH4 in bulk O2 because the relevant cluster ions are very weak and are declustered in the low-pressure declustering region normally used in an APIMS. O2 has a relatively low proton affinity, and protonated oxygen is expected to undergo proton transfer reactions with CO2, N2, and CH4. We report the use of H2, as a doping gas, in the source of an APIMS to facilitate the protonation of trace impurities in O2. For safety considerations, a buffer gas like He or Ar has to be added to keep the concentration of H2 below the lower explosion limit (LEL). Our results indicate a statistical limit of detection of 0.5 ppb for CH4, 0.3 ppb for CO2, and 1.2 ppb for N2.
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