Mass spectrometric and theoretical investigations into the formation of argon molecular ions in plasma mass spectrometry

Abstract

The a bundance and distribution of argon molecular ions (e.g., ArH', ArO', ArN', Ar,' and MAr'; M = metal) in plasma MS (ICP-MS, LA-ICP-MS and rf-GDMS) were investigated and compared. In ICP-MS the non-metal argon molecular ions were formed with higher intensity compared with the metal argide ions. This could be explained by theoretical calculations of the binding energies. The ArH' ion can be viewed as an isoelectronic system, comparable to HCI. The intensities of diatomic metal argide ions relative to metal ions in ICP-MS are less than A correlation between the intensities of metal argide ions with the bond dissociation energies of diatomic ions was found. The highest intensity of metal argide ions, of the order of per cent. values, were observed in rf-GDMS. The intensity of the argon molecular ions in an rf-GD varied by up to three orders of magnitude as a function of the plasma parameters (e.g., argon pressure in the GD ion source). The characteristic distribution of diatomic argide ions of REEs in ICP-MS was found to be comparable to the distribution of rare earth oxide ions.Keywords: Argon molecular ions; binding energy; inductively coupled plasma; mass spectrometry; metal argide; radiofrequency glow discharge Rare gases play an important role in all plasma techniques when they are used as the plasma gas, e.g., plasma-induced deposition, plasma sputtering and inductively or capacitively coupled plasma analytical methods such as plasma MS. Argon is normally used in these plasma techniques owing to the low price, the high purity that is available and the good plasma formation. The existence of argon molecular ions in these plasma techniques when using argon as the plasma gas can be proved, for example, by plasma MS,1-3 such as by GDMS or ICP-MS. Plasma MS methods were applied to the sensitive determination of trace and ultratrace elements or precise isotopic analysis of inorganic materials. The determination of chemical elements in the trace and ultratrace concentration range is often difficult and can be disturbed by isobaric interferences of analyte ions by molecular ions, such as argon ions, oxide, carbide, hydride or chloride molecular ions, formed in a plasma with elements of the matrix or residue gas. These interferences induce an increase in the detection limits. Therefore, knowledge of the intensities of molecular ions and their abundance and distribution is of specific interest for MS Journal of Analytical Atomic Spectrometry trace analysis of inorganic materials. Molecular ion formation processes, particularly diatomic ions with a non-metal, such as ArH', ArO'? ArN' and Arc', have been studied by numerous groups,4P7 owing to their high ion intensities and the risk of possible interferences in plasma MS. Sakata and Kawabata' found that the argon molecular ions are formed both in the plasma, owing to a positive plasma potential induced by capacitive coupling with the coil, and also behind the sampling cone, where a secondary discharge can exist. Because the relative intensities of the metal argide ion...

Metal argide (MAr+) ions are lost during ion extraction in laser ablation-inductively coupled plasma-mass spectrometry

“…Response ((c/s)/(mol/dm^3) Differences in the dissociation energies among MAr + ions may be influenced by both the electronegativity of the transition metal and electron configuration of the metal ion. It has been suggested that a more covalent-type interaction occurs between the metal ion and argon neutral for metals with higher electronegativities [17]. While this is a very weak covalent interaction for all transition metals with Ar, it would account for the higher MAr has a more complex ground state electron configuration.…”

In Situ Determination of First-Row Transition Metal, Ga and Ge Abundances in Geological Materials via Medium-Resolution LA-ICP-MS

“…The relative production of diatomic metal oxides (i.e., MO + /M + ) has been found to correlate with bond strengths (or bond dissociation energies) in studies of molecular ion formation during ICP‐MS analysis (e.g., Michiels and Gijbels 1984, Becker and Dietze 1995, 2000, Becker et al. 1996).…”

“…The production of diatomic argides has also been found to correlate with bond strengths (e.g., Barshick et al. 1995, Becker and Dietze 1997), and also with diatomic oxide production in a study of REE molecular ion formation during ICP‐MS analysis, albeit with MAr + /MO + on the order of < 10 −3 (Becker et al. 1996).…”

Radiofrequency glow-discharge devices for direct solid analysis

“…Also, the abundance and distribution of argon molecular ions (e.g. ArH + , ArO + , ArN + , Ar 2 + , and MAr + ) were compared for rf-GD-MS, ICP-MS, and laser ablation (LA)-ICP-MS [101]. The highest intensity of metal argide ions was observed in rf-GD-MS.…”