Higher-Order Multipole Ion Guide for Trapped Ion Mobility Spectrometers
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Solution Overview
Problem
Current trapped ion mobility spectrometers face limitations in ion storage capacity due to space charge effects, particularly for ions of low mobility, necessitating improved methods to increase the number of stored ions by a factor of three to five for enhanced identification rates in complex mixtures.
Innovation Solution
The implementation of an RF ion guide generating a higher-order multipole field (N>2) with a counteracting gas flow and adjustable electric DC field gradient allows for axial trapping and release of ions based on their mobility, utilizing a transition from higher-order to lower-order RF fields and varying gas flow velocities to enhance ion capacity and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a quadrupolar RF field (N=2) is used in the ion guide, then the device structure is simple and easy to manufacture, but the ion storage capacity is limited due to space charge effects
Solution Approach 1:
The patent changes the fundamental parameter of the RF field from quadrupolar (N=2) to higher-order multipole (N>2), which fundamentally alters the ion distribution pattern and eliminates space charge limitations, enabling storage of three to five times more ions
Solution Approach 2:
The patent transitions ions from on-axis positioning in quadrupolar fields to off-axis positioning in higher-order multipole fields, utilizing a different spatial dimension and distribution pattern to increase storage capacity
2Quantity of substance
If ions are trapped on-axis in a quadrupolar RF field, then the mobility resolution is high, but the ion storage capacity is limited
Solution Approach 1:
The patent inverts the conventional approach by trapping ions off-axis instead of on-axis in higher-order multipole fields, achieving both high storage capacity and maintained mobility resolution through this reversed spatial arrangement
3Quantity of substance
If the ion guide length is increased to store more ions, then the ion storage capacity increases, but the device size and complexity increase
Solution Approach 1:
The patent achieves increased ion storage capacity not by extending the ion guide length, but by changing the RF field configuration to higher-order multipole, which increases the effective storage volume within the same physical dimensions
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 significantly increases the ion storage capacity, achieving three to five times more ions than traditional quadrupolar systems while maintaining high mobility resolution, even at off-axis positions, and allows for efficient detection of multiple ion species.
Implementation Method 1
an RF ion guide (RF system) generates a radial quadrupolar RF field to hold ions near to the axis
Implementation Method 2
an electric DC field exhibits a slowly increasing ramp of an electric DC field barrier... the friction force of the moving gas equals the force of the electric DC field
Implementation Method 3
A moving gas drives entrained ions against the electric DC field barrier where the ions are axially trapped
Implementation Method 4
the ions are axially trapped and separated according to their mobilities at locations on the electric DC field ramp
Data Source
AI summary
The invention is related to a trapped ion mobility spectrometer (TIMS device) and proposes to use higher order (order N>2) linear multipole RF systems to accumulate and analyze ions at an electric DC field barrier, either pure higher order RF multipole systems or multipole RF systems with transitions from higher order towards lower order, e.g. from a linear octopolar RF system (N=4) to a linear quadrupole RF system (N=2) in front of the apex of the electric DC field barrier.