Tandem Multipole Ion Trap for Isobaric Mass Resolution
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Solution Overview
Problem
Conventional mass spectrometry techniques struggle to effectively isolate specific ion species from substantially isobaric ions with molecular weights differing by less than 1 amu, due to limitations in mass resolution and the impact of space charge, which distorts harmonic RF fields and changes the oscillation frequency of resonantly excited ions.
Innovation Solution
A method and system utilizing a tandem arrangement of multipole rod sets with differing RF waveforms and q values, generating a fringing field to radially confine and selectively eject ions, where an auxiliary AC waveform resonantly excites ions with a selected m/z, enhancing mass selectivity by repulsing unwanted ions and improving ion transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional isolation techniques (quadrupole filters or linear ion traps) are used to eliminate unwanted impurity ions, then the charge density is reduced, but the mass resolution is insufficient to resolve target ions from isobaric ions with molecular weights differing by less than 1 amu
Solution Approach 1:
The ion trap is divided into multiple trapping regions (first trapping region and second trapping region) separated by a barrier potential. This segmentation allows different ion populations to be trapped and processed in separate regions, enabling high-resolution mass analysis of target ions while independently managing impurity ions, thereby achieving both high mass resolution and effective charge density control
Solution Approach 2:
Different trapping regions are assigned different local conditions: the first trapping region is optimized for high-resolution mass analysis with specific RF and DC potentials, while the second trapping region handles impurity ion removal. The barrier potential creates localized separation, allowing each region to perform its specific function optimally without interfering with the other
2Quantity of substance
If higher charge density is maintained in the ion trap, then more ions can be analyzed, but space charge effects distort the harmonic RF fields and change the oscillation frequency of resonantly excited ions
Solution Approach 1:
By segmenting the ion trap into multiple regions with a barrier potential, the patent isolates the high-resolution analysis region from the impurity ion region. This allows high ion capacity in the overall system while maintaining frequency stability in the analysis region, as space charge effects are confined to the impurity region and do not interfere with resonantly excited ions in the analysis region
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables improved mass selectivity and ion isolation by effectively repelling and ejecting unwanted ions, reducing space charge effects and enhancing the resolution of ion separation, particularly for ions with small radial oscillation amplitudes, thereby improving the overall performance of mass spectrometry systems.
Implementation Method 1
RF fields can be generated within the first and second rod sets so as to radially confine the ions
Implementation Method 2
the RF fields interacting in an interaction region between the second end of the first rod set and the first end of the second rod set to produce a fringing field
Implementation Method 3
generating a barrier field at the second end of said second rod set so as to repel at least a portion of said ions away from the second end of the second rod set and toward the first rod set
Implementation Method 4
the auxiliary AC waveform having a frequency that substantially matches a secular frequency of the ions having the selected m/z
Implementation Method 5
a frequency that substantially matches a secular frequency of the ions having the selected m/z
Implementation Method 6
the auxiliary AC waveform generates a dipolar excitation field
Data Source
AI summary
A method is provided for processing ions in a multipole ion trap, comprising generating RF radial confinement fields within a first and second multipole rod set positioned in tandem, a ratio of q value exhibited by the second rod set relative to the first rod set being greater than one for any m/z, said RF axial confinement fields within the first and second rod sets interacting in an interaction region between the first and second rod sets so as to produce a fringing field; transmitting ions through said first rod set towards said second rod set; and increasing the radial oscillation amplitude of at least a portion of the ions within said first rod set such that at least a portion of said ions having an increased radial oscillation amplitude are repulsed by said fringing field.