Improved Atmospheric Pressure Ionization Mass Spectroscopic Methods: II . Extending the Range of Accuracy Through Nonlinear Calibration Techniques

The range of concentrations over which an atmospheric pressure ionization and mass spectroscopic (APIMS) can measure impurity levels in ultrahigh purity gases accurately has been extended from parts‐per‐trillion to parts‐per‐million levels using novel calibration methods. Nonlinear calibration relationships have been derived through kinetic models of the plasma reaction chemistry. These relationships account for background levels of impurities which cause curvature in log‐log plots of calibration data at low concentrations and correct for curvature induced by plasma saturation in high concentration regimes. Nonunity reaction orders such as have been documented for oxygen calibration in nitrogen also can be handled. These relationships have been fit using weighted nonlinear regression to calibration data that extend over ranges of concentration of more than five orders of magnitude. The resulting APIMS calibration relationships can be applied to analysis of unknown sample gases to provide quantitative analysis capability over wide ranges of concentration.