Progress of Cryogenics and Isotopes Separation , ISSN: 1582-2575
2011, Volume 14, Issue 1

Theoretical and Experimental Research of the Overlap Effects in the Quadrupole Mass Spectrometric Analysis of Hydrogen Isotopes Mixtures

Abstract

To measure the concentration of hydrogen isotopic species in gaseous streams of hydrogen isotopes mixtures sampled from a cryogenic separation column, we intend to use a GSD 320 quadrupole mass spectrometer. In order to consistently generate measurements of high precision and reliability, an extensive knowledge of instrumental effects and their underlying causes, and appropriate laboratory procedures for calibrating and performing the mass spectrometric analysis are required. The major problems of mass spectrometric isotopic analysis (especially in the case of hydrogen isotopes) are the overlap effects and contributions. Development of experimental procedures and correction algorithms for the mass 2 and mass 3 due to the following contributions to the peaks measured by the mass spectrometer: 

• H₃⁺ , HD⁺ contribution to mass 3 current;
• H₂⁺ and D⁺ contribution to mass 2 current

 Thus, the mass-to-charge 2 and 3 ion currents must be corrected for the presence of H₂⁺ and D⁺, H₃⁺ and HD⁺ respectively ions formed inside the ion source if an accurate measurement of HD concentration in the gas sample is to be made. The correction algorithms, the experimental procedures and the experimental results are presented in this work. The standard gas mixtures will be prepared in our laboratory by the pressure partial methode. We will use pure gases (H₂ and D₂) and equilibrated gas mixtures of H₂, HD and D₂ for mass-to-charge 2, 3 and 4 calibrations. The experimental set-up and procedure for equilibrating the gas mixtures, and concentrations calculus for the gas mixtures components (H₂, HD and D₂) are also presented in this paper.