Adsorption in Gas Mass Spectrometry. II. Effects on the Measurement of Isotope Amount Ratios.

The effects of adsorption in the mass spectrometer inlet system on the measured isotope amount ratios are discussed. A model is proposed to correct for these effects. The values of the isotope amount ratios obtained with the help of the model are about 1x10(exp-5) lower than the values obtained by linear extrapolation. The model enables to estimate the isotope fractionation factors involved in the effusion, adsorption and desorption processes.JRC.D-Institute for Reference Materials and Measurements (Geel