Once the ions have been separated by their mass-to-charge ratio, they must then be
detected or counted by a suitable detector. The fundamental purpose of the detector is to
translate the number of ions striking the detector into an electrical signal that can be
measured and related to the number of atoms of that element in the sample via the use of
calibration standards. Most detectors use a high negative voltage on the front surface of
the detector to attract the positively charged ions to the detector. Once the ion hits the
active surface of the detector, a number of electrons is released which then strike the next
surface of the detector, amplifying the signal. In the past several years, the channel
electron multiplier (CEM), which was used on earlier ICP-MS instruments, has been
replaced with discrete dynode type detectors (see Figure 6). Discrete dynode detectors
generally have wider linear dynamic ranges than CEMs, which is important in ICP-MS as
the concentrations analyzed may vary from sub-ppt to high ppm. The discrete dynode