Mass Spectrometric Evidence for Suprathermal Ionization in an Inductively Coupled Argon Plasma

Abstract

Mass spectra have been obtained of species in the axial channel of an inductively coupled argon plasma by extracting ions from the inductively coupled plasma into a vacuum system housing a quadrupole mass spectrometer. Ionization temperatures ( Tion) are obtained from relative count rates of m/z-resolved ions according to two general types of ionization equilibrium considerations: (a) the ratio of doubly/singly charged ions of the same element, and (b) the ratio of singly charged ions from two elements of different ionization energy. The Tion values derived from measurement of Ar+2/Ar+, Ba+2/Ba+, Sr+2/Sr+, and Cd+/I+ are all greater than those expected from excitation temperatures measured by other workers. The latter three values for Tion are in reasonable agreement with values obtained by optical spectrometry for a variety of argon inductively coupled plasmas.

A status report on helium inductively coupled plasma mass spectrometry

“…Subsenquently, Greenfield et al introduced mixtures of different molecular gases and argon or helium in the outer and the injector gas flows of the plasma torch to form mixed-gas ICPs for spectrochemical analysis [3]. These studies along with independent work by Fassel and associates [4] led to the development of Ar ICP-atomic emission spectrometry (Ar ICPAES), Ar ICP-atomic fluorescence spectrometry (Ar ICPAFS), and Ar ICP-mass spectrometry (Ar ICPMS) as viable techniques for elemental analysis [3][4][5][6][7][8][9]. Currently, Ar ICPAES and Ar ICPMS are the most dominant techniques for simultaneous multielement determinations, chiefly because they provide high selectivities and excellent powers of detection for many elements, wide concentration dynamic ranges, and low matrix effects on a relatively routine basis [1].…”

Fundamental studies of the plasma extraction and ion beam formation processes in inductively coupled plasma mass spectrometry

“…This discharge was called as "pinch" effect in the early work (112), it is now usually referred to as a secondary discharge. Douglas and French (113) found that the discharge is not a true electrogas dynamic effect but rather appears to be simply an electric arcing between the ICP and the sampling cone.…”

Fundamental studies of the extraction process in inductively coupled plasma mass spectrometry

“…Ionization temperature "isy be determined from the measurements of the relative intensities of atom and ion lines of a suitable species and the knowledge of the electron density, n^, via the Saha equation (39)(40)(41), provided the species available have sufficiently intense atomic and ionic lines. As an alternate method, ICF-MS can be employed to measure the ICP (42,43).…”