Ion Trap AGC via Variable Duty Cycle Gating
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Solution Overview
Problem
Conventional automatic gain control (AGC) methods in mass spectrometry are not applicable to temporally non-uniform ion sources, leading to saturation and space charge effects, which compromise detection accuracy and dynamic range.
Innovation Solution
A mass spectrometer configuration with a variable duty cycle is applied to pulsed ion beams from non-continuous ion sources, adjusting the duty cycle based on previous mass-resolved scans to minimize saturation and space charge effects, using a gating mechanism with frequencies ranging from 1 kHz to 1 GHz to control the number of ions and maintain detection limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional AGC methods use variable injection time to control ion number, then saturation and space charge effects are avoided in uniform ion beams, but the method becomes inapplicable to temporally non-uniform ion sources
Solution Approach 1:
The patent changes the control parameter from injection time to duty cycle. By modulating the gating signal duty cycle (the ratio of gate open time to total pulse period), the system can control the average ion flux into the trap regardless of the temporal distribution of ions from non-uniform sources. This parameter transformation makes AGC applicable to both uniform and non-uniform ion sources while maintaining detection accuracy through feedback control.
2Measurement precision
If high ion flux is used to improve signal intensity, then detection sensitivity increases, but saturation and space charge effects occur in the ion trap
Solution Approach 1:
The patent implements feedback control by measuring the ion signal intensity and using this information to adjust the gating duty cycle for subsequent ion injections. When the detected signal approaches saturation levels, the duty cycle is reduced to decrease ion flux. This closed-loop feedback mechanism maintains optimal ion population in the trap, preventing saturation and space charge effects while maximizing detection sensitivity through adaptive signal optimization.
3Quantity of substance
If long injection time is used to increase ion population in the trap, then signal intensity improves, but space charge effects increase and detection accuracy decreases
Solution Approach 1:
The patent transforms the static injection time parameter into a dynamic duty cycle control mechanism. Instead of using a fixed long injection time that always risks space charge effects, the system dynamically adjusts the duty cycle based on real-time ion population measurements. This allows the ion population to be optimized for each detection event, maintaining high signal intensity while preventing space charge effects that would degrade detection accuracy.
Data Source
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AI summary
An automatic gain control (AGC) technique and apparatus is introduced herein for any temporally non-uniform ion beam, such as, for example, an ion beam produced by a MALDI ion source so as to minimize space charge effects. The disclosed configurations and techniques can be achieved by using an ion optical gating element and applying a desired signal waveform (e.g., a square wave) having a predetermined duty cycle. The applied voltage amplitude of such a signal can be configured to switch between a voltage which fully transmits the ions, and a voltage which does not transmit any ions. The frequency is chosen to result in a period which is significantly lower than the smallest non-uniformity period. Techniques of the present invention can also be extended to methods of AGC which can use a single ion injection event from the ion source to avoid variations in ion numbers from an unstable ion source.