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

The abundance of metal argide (MAr+) ions during laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is measured during ablation of pure samples of transition metals. As expected, the relative abundance of MAr+ ions to M+ ions for various elements increases as the dissociation energy (D0) of the ion increases. Gas kinetic temperatures (Tgas) are determined from the calculated MAr+/M+ ratios and are used to indicate the origins of MAr+ ions. The determined Tgas values are very high, 8000 K to ≥ 20,000 K, which indicate that MAr+ ions are much less abundant in the mass spectrum than expected based upon plasma conditions. Collision-induced dissociation (CID) during the ion extraction process is suggested to be responsible for removal of MAr+ ions. Factors responsible for these collisions are discussed.

► MAr+ ions are less abundant than would be expected from Tgas conditions in the ICP.
► Errors in dissociation energies or mass bias do not account for the MAr+ abundances.
► Collision-induced dissociation of MAr+ ions during extraction is a likely cause.