Use of nitrogen and hydrogen in inductively coupled plasma mass spectrometry

Abstract

Small amounts of N₂ or H₂ were added at the main gas inlet to the Ar forming the plasma of an inductively coupled plasma mass spectrometer. Experiments involving either Ar–N₂ or Ar–H₂ plasmas were carried out using an r.f. coil with an outside diameter of 31 mm while the sampling depth (9.0 mm), torch to sampler cone distance (1.5 mm) and r.f. power (1000 W) were kept constant. Signal intensities for a wide range of elements were enhanced while Ba²⁺, Ce²⁺, BaO⁺, CeO⁺, MoO⁺, TiO⁺, WO⁺ and ZrO⁺ were maintained below 3% of their singly charged ions (M⁺). Signal enhancement was greater with the Ar–N₂ than the Ar–H₂ plasma. Whereas the use of an Ar–N₂ plasma was affected by interferences from polyatomic species of nitrogen, no significant increase in background signals was observed when the Ar–H₂ plasma was used. In general, the signal-to-background ratio was increased for a wide range of elements investigated when either the Ar–N₂ or Ar–H₂ plasma was employed.