Design considerations for a pressure-differential tandem source for use in atomic spectrometry
Factors that govern the likelihood of success of a tandem source formed from two devices that operate at different pressures are examined theoretically and experimentally. The union of an atmospheric-pressure inductively coupled plasma (ICP) with a reduced-pressure microwave induced plasma (MIP) is used to evaluate experimentally the theoretical arguments. For such a tandem source to be attractive, the loss in analyte number density in the lower-pressure second source must be compensated for by an offsetting gain in excitation or ionization efficiency or a reduction in background. These considerations are compared with what is found in the experimental ICP–MIP combination. At present, the ICP–MIP combination offers no improvement in detection limits or in ion to atom ratios over what is found in the ICP by itself. These considerations and comparisons suggest possible avenues for future research into pressure-differential tandem sources.