| 摘要 |
To control the filling of a trap in a mass spectrometer with the required number of ions, they are initially stored in a multi-pole ion guide. The filling level of the ions is measured to give a defined part-volume, in front of the ion trap for mass spectrometric analysis using ion cyclotron resonance (ICR). This controls the subsequent feed to the trap according to the store level. The ions held in the multi-pole guide are filtered by mass selection, acting as a multi-pole mass filter. The ion analysis uses a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer, or a high frequency ion trap mass spectrometer. A laser desorption ion (LDI) source is used, where the ions are passed directly into the holding zone of the multi-pole ion guide, through the action of a laser pulse on a sample. Matrix-supported laser desorbed ions (MALDI) are stored only partially in the multi-pole guide, where the matrix ions are filtered off and only the heavy ions for analysis remain in the ion guide. The ions can be formed from a sample by electro-spray ionizing, with systems to remove any solvent and reduce the pressure in the multi-pole guide as they are stored. To measure the number of ions stored in the multi-pole guide, a portion of the ions is fed to a detector for measurement of the electrical current. The detector is a secondary electron multiplier. The ion electrical current measurement can also be from a second multi-pole, as a measurement electrode, to be passed to the ion trap for the mass spectrometry measurement analysis. The ions can also be counted in the trap, where an ion release pulse is registered at electrodes to give a total electrical current measurement. The ion count can also be determined at an ion detector after the trap. An Independent claim is included for an apparatus to determine the number of ions in the intermediate store at the multi-pole guide, which has a sample carrier plate for laser desorption, a multi-pole ion guide directly in front of the carrier plate, a perforated diaphragm (9) as a final plate a to store the ions, and a switched potential supply for the diaphragm which is either a reflection potential to store the ions or an extraction potential to take out the ions.
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