Toward a fuller understanding of analytical atomic spectrometry

Although inductively coupled plasma emission and mass spectrometry have been in widespread use for a long time, there is still a gap in our knowledge concerning how atoms are formed in the ICP, by which mechanisms they are excited, how ionization occurs, and how these factors are influenced by operating parameters of the ICP such as gas flow rates, radiofrequency power, and viewing or sampling position. Furthermore it is still not clear how or whether the sampling cone of the mass-spectrometer interface affects the ICP itself. Although many measurements have been made downstream from the sampling orifice, less is clear about the influence of the interface upstream of the sampling process. In our laboratory is available a suite of measurement tools and techniques that are being exploited to address these questions. These techniques permit us to map, on a spatially resolved basis, such critical features as electron-energy distributions, gas-kinetic temperatures, ground-state analyte atom and ion number densities, electron concentrations, and densities of excited-state argon species. In turn, these parameters can be measured in the presence and absence of suspected interferents and in the presence and absence of an ICP-MS sampling cone. Here, the basis of these measurements will be described. Also, based on recent results, mechanisms of excitation of analyte atoms and ions will be proposed and the influence of the ICP-MS sampling cone will be examined.