INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY WITH AN ENLARGED SAMPLING ORIFICE AND OFFSET ION LENS .2. POLYATOMIC ION INTERFERENCES AND MATRIX EFFECTS

A new inductively coupled plasma mass spectrometer with an enlarged sampling orifice (1.31-mm dia.) and an offset ion lens yields very low levels of many troublesome polyatomic ions such as ArO+, ArN+, Ar2+, ClO+, and ArCl+. The signals from refractory metal oxide ions are approximately 1% of the corresponding metal ion signals, which is typical of most ICP-MS devices. Grounding the first electrode of the ion lens greatly reduces the severity of matrix effects to less than or similar to 20% loss in signal for Co+, Y+, or Cs+ in the presence of 10 mM Sr, Tm, or Pb. This latter lens setting causes only a modest loss (30%) in sensitivity for analyte elements compared to the best sensitivity obtainable by biasing the first lens. Alternatively, matrix effects can also be mitigated by readjusting the voltage applied to the first lens with the matrix present.