Mass spectrometric determination of trace oxygen

The calibration factor of the oxygen/argon ion current ratio has been found to depend on the background of the mass spectrometer in the 1–1000 ppm oxygen (in argon) range. Adsorption on the surface seems to be responsible for the phenomenon. Coverage‐dependent pumping speed of the surface is assumed in the interpretation of the results. By applying the background‐dependent calibration curve instead of a simple factor, accuracy greater than 10% can be achieved with substantially fewer calibration measurements.