The use of high resolution or magnetic sector mass spectrometers has become more common in ICP-MS, allowing the user to eliminate or reduce the effect of interferences due to mass overlap. Figure 2 shows a typical instrumental configuration used in high resolution (HR) ICP-MS. In this type of instrument, both a magnetic sector and an electric sector are used to separate and focus the ions. The magnetic sector is dispersive with respect to both ion energy and mass and focuses all the ions with diverging angles of motion coming from the entrance slit of the spectrometer. The electric sector is dispersive only to ion energy and focuses the ions onto the exit slit. Such an arrangement is called a double-focusing high resolution mass spectrometer. In ICP-MS, reverse Nier-Johnson geometry – where the magnetic sector is before the electric sector – is commonly used in order to decouple the electric fields in the electric sector from any electric field originating by the ICP RF generator.
The resolution of high-resolution instruments can be changed by adjusting the width of