title: Use of a clustering reaction to detect low levels of moisture in bulk oxygen using an atmospheric pressure ionization mass spectrometer.
abstract: Atmospheric 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 O(2), H(2)O, CO(2), and CH(4) in Ar, N(2), and He. However, it has not been successfully used to quantify trace impurities in bulk O(2) due to the low ionization potential of O(2). APIMS relies on charge-transfer reaction between the ions of the bulk gas molecules and impurity molecules. Since all the relevant impurity molecules have ionization potentials higher than that of O(2), APIMS has not been used to analyze for impurities in O(2). We report here the detection of sub-ppb levels of H(2)O in O(2) by making use of the clustering reaction between O(2)(+) and H(2)O. The declustering region in an APIMS, which is normally used to break apart unwanted and interfering clusters, has to be carefully adjusted to keep intact the weakly bound cluster O(2)(+)·H(2)O. Our results indicate a statistical detection limit of less than 300 ppt for the detection of H(2)O in O(2).
authors.affiliation: Air Products and Chemicals, Inc., 7201 Hamilton Boulevard, Allentown, Pennsylvania 18195.
authors.forename: A D
authors.initials: AD
authors.lastname: Scott
authors.forename: E J
authors.initials: EJ
authors.lastname: Hunter
authors.forename: S N
authors.initials: SN
authors.lastname: Ketkar