Adjusting the detector amplification in mass spectrometers
The amplification of secondary-electron multipliers in mass spectrometers is automatically adjusted by generating mass spectra with single ion signals, determining the average value of the peak heights of these single ion signals, and setting the amplification so that the average peak height assumes a desired nominal value. The amplification may be set via the supply voltage of the secondary-electron multiplier and can be increased or decreased by a desired factor using the known characteristic of the secondary-electron multiplier.
1. A method for adjusting the amplification of a secondary-electron multiplier in a mass spectrometer, the method being performed between analytical measurements of the mass spectrometer, comprising:
acquiring a mass spectrum with single-ion signals;
calculating an average peak height of the single-ion signals in the acquired mass spectrum; and
adjusting the supply voltage of the secondary-electron multiplier so that a desired nominal value for the average peak height is obtained.
2. The method of claim 1 , wherein a characteristic of the secondary-electron multiplier, representing the amplification as a function of supply voltage, is used during the adjusting of the supply voltage.
3. The method of claim 1 , further comprising prior to the acquiring a mass spectrum with single-ion signals, increasing the supply voltage of the secondary-electron multiplier to obtain peak heights of the single-ion signals recognizable above the electronic background noise for adjusting the supply voltage.
4. The method of claim 1 , wherein at least thirty single ion signals are used for the calculating of the average peak height of the single-ion signals.
5. The method of claim 1 , wherein the generation rate for ions in the ion source of the mass spectrometer is reduced for the acquisition of a mass spectrum with single-ion signals.
6. The method according of claim 1 , wherein the spatial and/or temporal focusing of the ions in the mass spectrometer is detuned for the acquisition of a mass spectrum with single-ion signals.
7. The method according of claim 1 , wherein the transmission of ions in the mass spectrometer is reduced for the acquisition of a mass spectrum with single-ion signals.
8. The method of claim 1 , wherein a controller for the mass spectrometer automatically reduces the ion current of the ion source, detunes the mass spectrometer, acquires mass spectra with single-ion peaks, computes the average peak height of the single-ion peaks, and adjusts the voltage of the secondary electron multiplier to such a value that a desired nominal average peak height value is obtained.
9. A method for adjusting the amplification of a secondary-electron multiplier in a mass spectrometer, the method being performed between analytical measurements of the mass spectrometer, comprising:
acquiring a mass spectrum with single-ion signals;
calculating an average peak height of the single-ion signals in the acquired mass spectrum; and
adjusting the supply voltage of the secondary-electron multiplier so that a desired nominal value for the average peak height is obtained,
wherein the generation rate for ions in the ion source of the mass spectrometer is reduced for the acquisition of the mass spectrum with single-ion signals.
10. A method for adjusting the amplification of a secondary-electron multiplier in a mass spectrometer, the method being performed between analytical measurements of the mass spectrometer, comprising:
acquiring a mass spectrum with single-ion signals;
calculating an average peak height of the single-ion signals in the acquired mass spectrum; and
adjusting the supply voltage of the secondary-electron multiplier so that a desired nominal value for the average peak height is obtained,
wherein at least one of the spatial focusing and temporal focusing of the ions in the mass spectrometer is detuned for the acquisition of the mass spectrum with the single-ion signals.
11. A method for adjusting the amplification of a secondary-electron multiplier in a mass spectrometer, the method being performed between analytical measurements of the mass spectrometer, comprising:
acquiring a mass spectrum with single-ion signals;
calculating an average peak height of the single-ion signals in the acquired mass spectrum; and
adjusting the supply voltage of the secondary-electron multiplier so that a desired nominal value for the average peak height is obtained,
wherein the transmission of ions in the mass spectrometer is reduced for the acquisition of the mass spectrum with single-ion signals.