Linear Ion Trap Quadrupole-Octopole Field for Space Charge Compensation
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Solution Overview
Problem
The performance of ion trap mass spectrometers is limited by space charge density, which affects mass accuracy and resolution, as the number of ions that can be analyzed without impacting analytical performance is restricted.
Innovation Solution
A two-dimensional substantially quadrupole field is established and maintained in a linear ion trap, comprising a quadrupole harmonic and an octopole harmonic, with the octopole harmonic amplitude significantly greater than other higher order harmonics, using auxiliary electrodes between pairs of rods to reduce space charge effects and improve mass accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a higher ion population is introduced to increase productivity, then the ion population increases, but space charge density increases which degrades mass accuracy and resolution
Solution Approach 1:
The patent applies parameter changes by introducing a controlled octopole harmonic component (A4) to the quadrupole field. This modifies the field parameters to create a non-linear field that compensates for space charge effects, allowing higher ion populations while maintaining mass accuracy. The specific parameter relationship A4/A2 between 0.01-5% optimizes this compensation effect.
Solution Approach 2:
The patent creates a composite electromagnetic field structure by combining quadrupole and octopole harmonics. This composite field configuration allows the system to benefit from both the mass filtering capability of the quadrupole and the space charge compensation of the octopole component, enabling higher ion populations without degrading performance.
2Productivity
If a higher ion population is introduced to increase productivity, then the ion population increases, but space charge density increases which degrades resolution
Solution Approach 1:
The patent modifies field parameters by adding an octopole harmonic component to the quadrupole field. This parameter change creates a non-linear field that counteracts space charge-induced ion cloud expansion, thereby maintaining resolution even at higher ion populations.
Solution Approach 2:
The patent employs a composite field structure combining quadrupole and octopole harmonics. This composite configuration enables the system to handle higher ion populations while preserving resolution by using the octopole component to compensate for space charge effects that would otherwise degrade resolution.
3Measurement precision
If auxiliary electrodes are added to create octopole harmonic to improve mass accuracy, then mass accuracy improves, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the electrode structure into main quadrupole rods and auxiliary electrodes. The auxiliary electrodes are positioned to specifically generate the octopole harmonic component, separating the quadrupole field generation and octopole field generation into distinct structural elements that work together.
Solution Approach 2:
The auxiliary electrodes serve multiple functions: they generate the octopole harmonic component for space charge compensation, work in conjunction with the main rods to create the composite field, and can be integrated into existing quadrupole structures. This multi-functionality reduces the need for entirely separate systems.
4Object-affected harmful factors
If octopole harmonic amplitude is increased to minimize space charge effects, then space charge compensation improves, but other higher order harmonics may increase which could degrade performance
Solution Approach 1:
The patent precisely controls the parameter relationship between octopole (A4) and quadrupole (A2) harmonics, maintaining A4/A2 between 0.01-5%. This parameter optimization ensures sufficient octopole component for space charge compensation while keeping other higher order harmonics (A6, A8, etc.) at least ten times smaller than A4, preventing performance degradation.
Solution Approach 2:
The patent applies local quality by creating a non-uniform field distribution through the octopole component. The field has different characteristics at different radial positions, with the octopole harmonic providing localized field modifications that compensate for space charge effects specifically where they occur most strongly.
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 enhances mass accuracy and resolution by minimizing the impact of space charge density, allowing for a higher ion population without degrading mass spectrometer performance, as demonstrated by maintaining a quadrupole field with a substantial octopole component and minimal higher order components.
Implementation Method 1
establishing and maintaining a two-dimensional substantially quadrupole field, the field comprising a quadrupole harmonic of amplitude A2 and an octopole harmonic of amplitude A4
Implementation Method 2
establishing and maintaining a two-dimensional substantially quadrupole field
Implementation Method 3
providing i) a first RF voltage to the first pair of rods at a first frequency and in a first phase, ii) a second RF voltage to the second pair of rods at a second frequency equal to the first frequency and in a second phase, opposite to the first phase
Implementation Method 4
providing a dipolar excitation AC voltage to either the first pair of rods or a diagonally oriented pair of auxiliary electrodes at a lower frequency than the first frequency to radially excite the selected portion of the ions
Data Source
AI summary
A two-dimensional substantially quadrupole field is provided. The field comprises a quadrupole harmonic of amplitude A2 and an octopole harmonic of amplitude A4, wherein A4 is greater than 0.01% of A2, A4 is less than 5% of A2, and, for any other higher order harmonic with amplitude An present in the field, n being any integer greater than 2 except 4, A4 is greater than ten times An.