Ion Signal Frequency Analysis for Noise-Robust Charge Determination
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Solution Overview
Problem
The accuracy of ion charge determination in image-charge/current type mass analyzers is severely deteriorated by electronic noise, leading to poor mass spectra due to the high level of noise in the measurement circuits, which is costly and complex to mitigate with current methods requiring high vacuum states and bespoke circuit designs.
Innovation Solution
A method to estimate the mass of a molecule by measuring the mass loss due to neutral loss species during oscillatory motion, causing a frequency change in the image-charge/current signal, allowing for more accurate mass determinations despite electronic noise, without the need for complex electronics or cryogenic cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct image-charge/current signal measurement is used to determine ion charge, then the measurement process is simple, but the accuracy is severely deteriorated by electronic noise
Solution Approach 1:
The patent converts the harmful effect of electronic noise into a beneficial approach by abandoning direct amplitude measurement (which is noise-sensitive) and instead using frequency measurement of oscillatory signals. The method leverages the fact that frequency can be determined very precisely even in noisy environments, and uses the relationship between oscillation frequency and mass-to-charge ratio to indirectly determine ion charge through neutral loss detection, thereby converting the noise problem into a solvable measurement challenge.
Solution Approach 2:
The patent introduces an intermediary measurement approach: instead of directly measuring ion charge (which is affected by noise), it measures the frequency of oscillatory motion as an intermediary parameter. This frequency measurement serves as a mediator that is not affected by electronic noise, and through the known relationship between frequency and mass-to-charge ratio, allows indirect determination of ion charge with high precision.
2Measurement precision
If high vacuum states and bespoke circuit designs are used to mitigate electronic noise, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex electronic mitigation systems (high vacuum states, bespoke circuit designs) with a simpler measurement approach based on frequency analysis. Instead of using complex mechanical/electronic systems to reduce noise, it substitutes a purely analytical method that determines charge from frequency measurements, thereby achieving high accuracy without increasing device complexity.
Solution Approach 2:
The patent changes the measurement parameter from amplitude (which is noise-sensitive) to frequency (which is noise-resistant). By measuring the frequency of oscillatory signals rather than their amplitude, the system achieves high precision charge determination without requiring complex noise mitigation infrastructure, thus avoiding increased device complexity and cost.
3Ease of operation
If ion charge is determined from image-charge/current signal amplitude, then the measurement process is straightforward, but accuracy is poor due to noise
Solution Approach 1:
The patent inverts the conventional measurement approach: instead of determining charge directly from signal amplitude (the straightforward but inaccurate method), it determines charge indirectly from signal frequency. This inversion of the measurement paradigm maintains operational simplicity while dramatically improving accuracy, as frequency determination is not degraded by electronic noise.
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 improves the accuracy of ion mass measurements by leveraging frequency changes caused by neutral loss, providing higher accuracy mass spectra without the need for expensive or complex equipment, thus overcoming the limitations of current noise-affected systems.
Implementation Method 1
Detection of ions using image charges is based on principles derived by Shockley and Ramo. Here, it was shown that a measurable current is induced in an electrode by the image of a moving charge passing by that electrode.
Implementation Method 2
The frequency of ion motion depends on its mass-to-charge (m/z) ratio, and where multiple packets of ions exist within an ion analyser (e.g., ion trap), the motion of each packet of ions with the same m/z ratio may be synchronous as provided by the focusing properties of an ion analyser.
Implementation Method 3
The induced image-charge current, I, is given by the rate of change of this quantity as follows: I = dQ/dt = Qv/d. The induced image-charge/current is a sinusoidal oscillatory signal of the form: I(t) = I0 sin(ωt), where I0 is the amplitude proportional to the charge Q of the ion.
Data Source
AI summary
A method of processing data determined from an image-charge/current signal representative of ions of a given charge state (Q) undergoing oscillatory motion of a respective oscillation frequency (ω) within an ion analyser apparatus. The method comprises acquiring a data set comprising a first measured signal frequency (ω1) associated with a first part of a measured image-charge/current signal of an ion and a second measured signal frequency (ω2) associated with a subsequent second part of the measured image-charge/current signal of the ion. The method includes estimating a charge state (Q) of the ion undergoing oscillatory motion of said first measured signal frequency (ω1) and subsequently of said second measured signal frequency (ω2) and therewith estimating the value of a mass change Δm to substantially match a reference mass corresponding to a mass of one or more neutral loss. The method includes estimating the mass (M) of a deprotonated molecule forming a part of the ion according to the estimated charge state (Q) of the ion, the first measured signal frequency (ω1), the quantified mass change value Δm, and the mass-to-charge ratio (mp/e) of a protonating proton.