Mass spectrometric ion storage device for different mass ranges
The invention relates to devices and methods for the storage of ions in mass spectrometers. The invention proposes the generation and superposition of two multipole fields of different order, independent of each other, in an RF multipole rod system. In an embodiment with eight pole rods, for example, it is thus possible to jointly store low-energy electrons in a central RF quadrupole field, which effectively acts only on electrons and holds them together radially, on the one hand, and multiply charged heavy positive ions in an RF octopole field, which effectively acts only on the ions, on the other hand, in order to fragment the positive ions by electron capture dissociation (ECD). In a different embodiment, multiply charged positive analyte ions and suitable negative reactant ions can react with each other in an octopole field by electron transfer dissociation (ETD) with a high fragmentation yield, and the fragment ions can subsequently be bundled by a transition to a quadrupole field to form a fine ion beam, which can leave the multipole rod system axially. A mixture of hexapole and dodecapole systems is also possible.
1. A method for the operation of a reaction cell for charged particles, comprising:
supplying an RF multipole rod system with at least eight pole rods with RF voltages so that a pseudo-quadrupole potential for the radial storage of charged particles having low charge-related mass m/z is produced in the interior, and a pseudo-octopole, or a pseudo-multipole potential of higher order, for the radial storage of charged particles with significantly higher charge-related mass m/z is superimposed on the pseudo-quadrupole potential,
where the RF voltage for the pseudo-quadrupole potential is chosen to store electrons, and the RF voltage for the pseudo-octopole, or pseudo-multipole potential, is chosen to store ions with a charge-related mass m/z greater than or equal to about 50 daltons.
2. The method according to claim 1 , wherein the stored electrons and the stored ions react via electron capture dissociation (ECD).
3. The method according to claim 2 , further comprising a magnetic field generator that provides for a magnetic field parallel to an axis of the RF multipole rod system in order to promote electron capture dissociation reactions.
4. The method according to claim 2 , wherein the electrons have a kinetic energy of less than 15 electronvolts.
5. The method according to claim 1 , wherein the RF voltage for the pseudo-quadrupole potential comprises a frequency of about 200 megahertz and an amplitude of about 100 volts, and the RF voltage for the pseudo-octopole, or pseudo-multipole potential, comprises a frequency of about 1 megahertz and an amplitude of about 500 to 1000 volts.
6. The method according to claim 1 , further comprising an electron generator that supplies electrons to the RF multipole rod system.
7. The method according to claim 6 , wherein a large excess of electrons is generated and supplied to the RF multipole rod system so that a continuous flow of electrons results therein.
8. The method according to claim 6 , wherein the electron generator comprises one of a hairpin thermionic cathode and a photoelectron emitter.
9. The method according to claim 6 , wherein an inner pole rod surface is irradiated with light over a large area in order to produce photoelectrons.
10. The method according to claim 6 , wherein ionizable molecules are irradiated with light in order to produce electrons.
11. The method according to claim 1 , wherein the electrons are one of introduced axially into the RF multipole rod system and generated on an axis thereof.
12. A method for the operation of a reaction cell for ions, comprising:
supplying an RF multipole rod system with at least eight pole rods with RF voltages so that a pseudo-quadrupole potential for the radial storage of ions having low charge-related mass m/z is produced in the interior, and a pseudo-octopole, or a pseudo-multipole potential of higher order, for the radial storage of ions with significantly higher charge-related mass m/z is superimposed on the pseudo-quadrupole potential,
wherein the charge-related masses m/z of the two ion types differ by more than factor twenty, and
wherein the RF voltage for the pseudo-quadrupole potential is chosen to store the ions having low charge-related mass m/z, and the RF voltage for the pseudo-octopole, or pseudo-multipole potential, is chosen to store the ions of higher charge-related mass m/z so that the two ion types are stored simultaneously within the RF multipole rod system.