Harmonic Electrostatic Ion Trap for Accurate STORI-Based CDMS
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Solution Overview
Problem
Existing ion trap charge detection mass spectrometry (CDMS) instruments face challenges such as anharmonic potential leading to poor m/z measurement accuracy, non-sinusoidal signal processing reducing sensitivity, and inability to analyze multiple ion species simultaneously due to desolvation issues and ion decay during measurement.
Innovation Solution
An electrostatic trap with non-oscillatory voltages applied to electrodes for harmonic ion motion, generating a Selective Temporal Overview of Resonant Ion (STORI) plot to determine ion charge and mass-to-charge ratio, allowing for simultaneous analysis of multiple ion species and minimizing errors from ion decay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Fourier transform analysis is used to process the inductive detector signal, then the signal can be analyzed, but the sensitivity is significantly reduced due to signal distribution among numerous harmonics
Solution Approach 1:
The patent extracts only the fundamental frequency component from the detector signal using bandpass filtering, rather than performing full Fourier transform analysis. This isolates the primary oscillation signal at frequency f0, eliminating the distribution of signal energy across multiple harmonics and significantly improving detection sensitivity while reducing processing complexity
Solution Approach 2:
Instead of transforming the time-domain signal to frequency domain (Fourier transform), the patent inverts the approach by directly filtering and analyzing the fundamental frequency component in the time domain, then using the oscillation frequency to determine m/z ratio. This reversal avoids the sensitivity loss inherent in full spectral analysis
2Measurement precision
If opposing electrostatic mirrors are used to determine ion m/z from oscillation frequency, then charge can be measured, but the anharmonic potential causes poor m/z measurement accuracy
Solution Approach 1:
The patent changes the fundamental parameter of the trapping potential from anharmonic (opposing mirrors) to harmonic (quadrupole field). By using a quadrupole mass filter configuration with RF and DC voltages on four rods, the system creates a truly harmonic potential well where oscillation frequency is directly proportional to sqrt(q/m), enabling accurate m/z measurement independent of initial kinetic energy
Solution Approach 2:
The patent replaces the mechanical mirror-based trapping system with an electromagnetic quadrupole field system. This substitution creates a more ideal harmonic potential that is less sensitive to positioning errors and provides more accurate frequency-based mass measurement
3Measurement precision
If ions are moved directly from source to mirrors without desolvation, then the measurement process is simplified, but mass shifts occur during measurement as ions lose solvent
Solution Approach 1:
The patent performs desolvation as a preliminary action before the ions enter the measurement region. A heated capillary and desolvation region remove solvent molecules from the electrospray ions prior to their introduction into the quadrupole trap, ensuring that the measured mass remains stable throughout the analysis period without further solvent loss
4Productivity
If a single ion species is analyzed at a time, then signal processing is simplified, but acquisition cycles become very long
Solution Approach 1:
The patent enables continuous analysis of multiple ion species by using the quadrupole trap to simultaneously confine and analyze multiple ions with different m/z ratios. The system continuously monitors oscillation frequencies of all trapped ions and uses bandpass filtering to extract signals from multiple species, dramatically increasing productivity while maintaining measurement precision through frequency-based separation
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
Improves m/z measurement accuracy, increases system sensitivity, and enables simultaneous analysis of multiple ion species, reducing errors associated with ion decay and desolvation.
Implementation Method 1
an electrostatic trap to establish a trapping field that causes the trapped ions to undergo harmonic motion along a longitudinal axis
Implementation Method 2
the trapped ions to undergo harmonic motion along a longitudinal axis
Implementation Method 3
an image current detector that generates a time-varying signal (also referred to as a transient) responsive to the longitudinal motion of the ions
Data Source
AI summary
Apparatus and methods for performing charge detection mass spectrometry for measurement of the mass of a single ion of interest are disclosed. The ion of interest is caused to undergo harmonic oscillatory movement in the trapping field of an electrostatic trap, such that an image current detector generates a time-varying signal representative of the ion's oscillatory movement. This time-varying signal (transient) is processed (e.g., via a Fourier transform) to derive the ion's frequency and consequently determine the ion's mass-to-charge ratio (m/z). Ion charge is determined by construction of a Selective Temporal Overview of Resonant Ion (STORI) plot, which tracks the temporal evolution of signals attributable to the ion of interest, and where the slope of the STORI plot is related to the charge. The STORI plot may also be employed to identify ion decay events during transient acquisition and/or the presence of multiple ions of the same mass or non-resolvable ions.