The detector in the LC/MS is a high-energy-dynode (HED) electron multiplier. The detector receives the ions exiting the quadrupole mass filter. It generates a signal current proportional to the number of ions it receives. This signal is passed to the electronics for amplification and processing.
The EMV is the voltage applied to the electron multiplier.
All active components of the HED electron multiplier are located out of the direct path from the end of the mass filter. This greatly reduces the noise caused by neutral particles.
The HED electron multiplier receives an input current generated by the ions striking it, amplifies that current, and generates a proportional output current.
Gain = Output current / input current
Gain is controlled by the electron multiplier voltage (EMV). If you raise the EMV, the gain increases. The relationship between EMV and gain is log linear. This linear relationship is common for all multipliers. Since the slope of this line is constant, the only adjustment that needs to be made is to the intercept. The gain calibration routine simply adjusts the value of the intercept for the specific instrument. The instrument-specific gain curve coefficients are then stored in the LC/MS.
| Minimum | Maximum | Default |
|---|---|---|
| 0 | 3000 V | 1240 V |
See Also