Consideration of Highly-efficiency Ionization Using Helium Glow Discharge Ion Source

Abstract

High-effective ionization during ferrous analyses using a He glow-discharge ion source was investigated. The respective relationships between the ionization potential (Ip) of each element and various ionic strengths were studied in detail for He glow discharge and Ar glow discharge. The energies of the helium metastable atom (He^m) is 1910 kJ/mol (19.80 eV) and 2022 kJ/mol (20.96 eV). It is presumed that He^m contributes to creation of doubly-charged and singly-charged ions. Results show that numerous doubly-charged ions are generated by He glow discharge. If this ratio is greater than that of an internal standard element Fe, the RSF-value becomes greater than 1 (the ionic strength ratio decreases). Furthermore, with elements having Ip₂ of more than approximately 18 eV, e.g., Ni, As, P, and C, the relative ionic strength of doubly-charged ion with respect to the singly-charged ion is only several percent at the highest. Consequently, the RSF-values approach unity (1). High-effective ionization by glow discharge is dependent upon the type of discharge gas, the matrix (internal standard element) and analyzing element, the presence of spectral interference, RSF-value, and other factors.