Segmented Ion Guide Mass Analyzer Pseudo-Potential Barriers
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Solution Overview
Problem
Existing ion guides in mass spectrometers face instability issues due to changes in oscillating electric fields, leading to radial instabilities and resonance effects, which result in ions being lost from the system, particularly affecting ions with specific mass-to-charge ratios.
Innovation Solution
A mass analyzer with a segmented ion guide comprising multiple electrodes, where a first AC voltage creates pseudo-potential barriers with a specific amplitude along the axial length, and a second AC voltage with a different amplitude is applied to selectively trap or eject ions based on their mass-to-charge ratios, allowing for sequential ejection in order of their mass-to-charge ratio or in reverse order.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an RF voltage is applied to confine ions radially within the ion guide, then ion confinement is improved, but radial instabilities and resonance effects occur leading to ion loss
Solution Approach 1:
The ion guide is divided into multiple electrode segments along the axial direction, with each segment independently controllable. This segmentation allows different voltage patterns to be applied to different segments, enabling localized correction of instabilities and preventing resonance effects from propagating through the entire guide.
Solution Approach 2:
The patent employs dynamic voltage control where the RF voltage amplitude and phase are continuously adjusted based on detected ion behavior. This dynamic adjustment allows the system to adapt to changing conditions and prevent the development of radial instabilities and resonance effects.
2Productivity
If a static axial electric field is used to propel ions along the axis, then ion transport efficiency is improved, but low mass-to-charge ratio ions are blocked by pseudo-potential barriers
Solution Approach 1:
The patent applies periodic RF voltage pulses in conjunction with the static axial field. These periodic pulses create temporary reductions in the pseudo-potential barriers at strategic locations, allowing low mass-to-charge ratio ions to pass through while maintaining efficient transport for all ion types during the pulse cycles.
Solution Approach 2:
The system dynamically adjusts the amplitude and frequency parameters of the RF voltage based on the mass-to-charge ratio distribution of ions in the beam. By changing these parameters, the pseudo-potential barrier heights are modulated to permit passage of previously blocked low mass-to-charge ratio ions while maintaining overall transport efficiency.
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 solution enhances the stability and efficiency of ion transmission by effectively confining and selectively ejecting ions, reducing radial instabilities and resonance effects, thereby improving the overall performance of the mass spectrometer.
Implementation Method 1
A minimum in the electric field is commonly referred to as a pseudo-potential well or valley. RF ion guides are designed to exploit this phenomenon by causing a pseudo-potential well to be formed along the central axis of the ion guide so that ions are confined radially within the ion guide.
Implementation Method 2
It is also well known that the time averaged force on a charged particle or ion due to an AC inhomogeneous electric field is such as to accelerate the charged particle or ion to a region where the electric field is weaker.
Implementation Method 3
It is known to use a radio frequency (RF) transport ion guide operating at an intermediate pressure of around 10−3-101 mbar to transport ions through a region maintained at an intermediate pressure.
Data Source
AI summary
An ion guide or mass analyser is disclosed comprising a plurality of electrodes having apertures through which ions are transmitted in use. A pseudo-potential barrier is created at the exit of the ion guide or mass analyser. The amplitude or depth of the pseudo-potential barrier is inversely proportional to the mass to charge ratio of an ion. One or more transient DC voltages are applied to the electrodes of the ion guide or mass analyser in order to urge ions along the length of the ion guides or mass analyser. The amplitude of the transient DC voltage applied to the electrode may be increased with time so that ions are caused to be emitted from the ion guide or mass analyser in reverse order of their mass to charge ratio.