Studies on Spectroscopic and Non-spectroscopic Interferences in Inductively Coupled Plasma Mass Spectrometry

In this study, the mechanisms of spectroscopic interference (spectral overlap caused by interfering ion species) and non-spectroscopic interference (matrix effect) in inductively coupled plasma-mass spectrometry (ICP-MS) were clarified. Interfering ion species were classified into two group: refractory oxide (MO⁺) and Ar polyatomic ions (ArX⁺ X=:H,C,O,N). The MO⁺ resulted from the ionization of undissociated neutral oxides in the ICP. A higher plasma temperature and/or the lower partial pressure of oxygen in the ICP would be required to reduce the formation of oxide ion species. The formation of ArX⁺ was related to a collision-induced reaction of Ar with X⁺ occurring at the interface region between the sampling and the skimmer cones, and the use of shielded ICP suppressed the collision. In ICP-MS coupled with the electrothermal vaporization (ETV>) technique, independent matrix effects were observed. One was "signal enhancement caused by hydrogen mixed with argon carrier gas"; the other was "signal enhancement caused by a halogen matrix". Both signal-enhancement effects resulted from the promotion of ionization of analytes through a charge-transfer reaction and/or electron impact in the interface plasma not in the ICP.