EFFECT OF SAMPLER AND SKIMMER ORIFICE SIZE ON ANALYTE AND ANALYTE OXIDE SIGNALS IN INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

The size of the orifice in the sampling cone of the interface in an inductively coupled plasma-mass spectrometer (ICP-MS) has a major impact on signal characteristics. In particular, for oxide forming elements, the MO+/M+ ratio is very dependent on orifice size. This is illustrated for a range of elements (La, Ho and Yb) as a function of nebulizer gas flow and for sampling cone orifice sizes ranging from 0.51 to 0.94 mm. In addition the size of the sampling orifice changes the shape of the signal vs nebulizer flow rate plot and this is illustrated. A curious and important observation is that the signal dependence on nebulizer flow rate is essentially identical for all analytes at any one orifice size if the analyte and analyte oxide (when observed) responses are summed. This indicates that the sampling orifice is the primary location of oxide formation in ICP-MS. Finally the effect of the skimmer orifice diameter on analyte signals is also illustrated for orifice diameters of 0.76, 0.89 and 1.0 mm in conjunction with sampling orifice sizes ranging from 0.51 to 0.94 mm. © 1990.