Mixed radio frequency multipole rod system as ion reactor
The invention relates to a linear multipole ion storage device which is suitable for reactions between positive and negative ions, and for fragmentation reactions by electron transfer dissociation (ETD) in particular. The invention uses a linear RF ion trap with at least three pairs of rods with a new type of electronic power supply. The two phases of a first RF voltage are applied to the pole rods alternately around the circumference and confine positive as well as negative ions in the radial direction. A second RF voltage is either applied single-phase to some of the pole rods, but not to all of them, or two-phase to unequal numbers of pole rods so that the axis potential oscillates with the frequency of this second RF voltage and generates a pseudopotential barrier which acts axially on ions of both polarities at the ends of the ion storage device. In the interior, the second RF produces a complex superposition field resulting in an increased fragmentation yield for ETD.
1. A linear RF ion trap with a plurality of pole rods which are supplied alternately around the circumference with both phases of a first RF voltage, comprising:
a single phase of a second RF voltage is supplied to some but not all of the plurality of pole rods, or one phase of a second RF voltage is applied to a first group of the plurality of pole rods, and the other phase of the second RF voltage is supplied to a second group of the plurality of pole rods, the two groups of pole rods not being equal in number.
2. A linear RF ion trap according to claim 1 , wherein the distribution of the second RF voltage to the pole rods is spatially symmetric to the axis.
3. A linear RF ion trap according to claim 1 , wherein the distribution of the second RF voltage to the pole rods is spatially asymmetric to the axis.
4. A linear RF ion trap according to claim 1 , wherein the second RF voltage can be switched off.
5. A linear RF ion trap according to claim 1 , wherein the ion trap comprises terminating electrodes at both ends.
6. A linear RF ion trap according to claim 5 , wherein the terminating electrodes comprises apertured diaphragms.
7. A linear RF ion trap according to claim 6 , wherein the apertured diaphragms are domed.
8. A linear RF ion trap according to claim 5 , wherein the terminating electrodes have the form of adjacent ion guides.
9. A linear RF ion trap according to claim 1 , wherein the pole rods comprise a non-conducting high-resistivity layer and a power supply generates a potential gradient along the pole rods.
10. A linear RF ion trap according to claim 1 , wherein the ion trap is divided into segments by a segmentation of the pole rods.
11. A linear RF ion trap according to claim 10 , wherein a supply device for the pole rods with voltages in the segments of the ion trap can supply separately adjustable axis potentials.
12. A linear RF ion trap with a plurality of pole rods which are supplied alternately around the circumference with both phases of a first RF voltage, comprising:
a second RF voltage is supplied in an asymmetrical way to some or all of the pole rods in such a way that a residual RF potential remains in the axis of the linear ion trap.