ZONE MODEL AS AN EXPLANATION FOR SIGNAL BEHAVIOR AND NON-SPECTRAL INTERFERENCES IN INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The zone model is a simplified representation of the plasma, resulting from the findings of an optimization study for a VG PlasmaQuad PQ1 in ductively coupled plasma (ICP) mass spectrometer (VG Elemental, Winsfo rd, Cheshire, UK). According to this model, for every nuclide there is a zone in the central channel of the ICP, where a maximum density of singly charged ions occurs. The position of such a zone of maximum Mdensity is a function of the mass number of the nuclide and the zone c an undergo a spatial displacement under the influence of an alteration of an instrumental parameter or the introduction of a different matri x. This representation not only enables an explanation of a large numb er of observations from the optimization study, but also allows an und erstanding of why both matrix induced signal suppression and enhanceme nt were observed, why for a given matrix the extent to which the signa l intensities were altered differed from day to day and finally why th e extent to which a signal is influenced by the matrix was seen to be a function of the mass number of the corresponding nuclide. Although t he zone model might not completely reflect the genuine physical realit y in all its facets, it provides a phenomenological model for the vari ation of ion signals with mass number, operating parameters and matrix composition.