Ion Funnel Low-Mass Filter for Mass Spectrometry
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Solution Overview
Problem
Existing analytical instruments face challenges with excessive space charge effects, which distort electric fields, reduce mass measurement accuracy, and cause unwanted fragmentation, particularly due to low-m/z ions, and current strategies fail to effectively distinguish ions of interest from background ions.
Innovation Solution
A method and apparatus utilizing a filtering plate or electrode within an ion funnel, biased with adjustable DC voltage to generate a barrier potential, preventing low-m/z ions from exiting, thereby reducing space charge effects and enhancing instrument performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If data-dependent corrections and automated methods are used to regulate ion populations, then mass measurement accuracy is improved, but space charge effects cannot be fully reduced and ions of interest cannot be distinguished from background ions
Solution Approach 1:
The patent segments the ion population by mass-to-charge ratio using a dual quadrupole system. The first quadrupole acts as a mass filter to separate background ions (low m/z) from analyte ions (high m/z), allowing selective transmission of ions of interest while rejecting space charge-contributing background ions. This segmentation resolves the contradiction by physically separating ion populations rather than relying on post-acquisition corrections.
Solution Approach 2:
The patent applies preliminary mass filtering in the first quadrupole before ions enter the second quadrupole and mass analyzer. By pre-filtering out background ions that contribute to space charge effects, the system prevents these harmful effects from occurring in the main analyzer, rather than attempting to correct them after they have distorted measurements.
2Productivity
If low m/z ions are allowed to pass through the ion funnel, then ion transmission is maximized, but space charge effects increase causing electric field distortion and measurement errors
Solution Approach 1:
The dual quadrupole system segments ions by mass-to-charge ratio, allowing the system to selectively transmit only high m/z analyte ions while blocking low m/z background ions. This resolves the contradiction by maintaining ion transmission for relevant species while eliminating transmission of space charge-contributing ions, achieving both productivity and reduced harmful factors simultaneously.
Solution Approach 2:
The patent applies different transmission characteristics to different mass ranges within the ion beam. The first quadrupole is configured with specific RF and DC voltages to create a mass-selective transmission window, allowing high m/z ions to pass while blocking low m/z ions. This local quality differentiation resolves the contradiction by optimizing transmission for analyte ions while preventing space charge effects from background ions.
3Object-affected harmful factors
If a mass filter is added to selectively remove background ions, then space charge effects are reduced, but device complexity increases
Solution Approach 1:
The patent merges the mass filtering function with the existing ion guide system by using the first quadrupole in a mass-filtering mode while the second quadrupole operates as the main ion guide and analyzer. This integration allows space charge reduction through mass-selective filtering without adding a completely separate filtering apparatus, thereby reducing the increase in device complexity compared to adding entirely independent filtering systems.
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
The solution effectively filters low-m/z ions, reducing space charge and improving mass spectrometer performance by selectively eliminating background ions, allowing for more accurate analysis and dynamic adjustment based on sample properties.
Implementation Method 1
Voltages when applied to the filtering plate or electrode generate a barrier potential prohibiting ions introduced to the funnel from exiting the funnel having a kinetic (m/z) energy lower (i.e., lower mass-to-charge ratio) than the barrier potential
Implementation Method 2
In a population of ions, electric fields of the ions influence each other and the collective effect is known as space charge. The detrimental effects of excessive space charge on instrumental performance are well known in the art. For example, like-charged ions repel each other
Data Source
AI summary
An adjustable, low mass-to-charge (m/z) filter is disclosed employing electrospray ionization to block ions associated with unwanted low m/z species from entering the mass spectrometer and contributing their space charge to down-stream ion accumulation steps. The low-mass filter is made by using an adjustable potential energy barrier from the conductance limiting terminal electrode of an electrodynamic ion funnel, which prohibits species with higher ion mobilities from being transmitted. The filter provides a linear voltage adjustment of low-mass filtering from m/z values from about 50 to about 500. Mass filtering above m/z 500 can also be performed; however, higher m/z species are attenuated. The mass filter was evaluated with a liquid chromatography-mass spectrometry analysis of an albumin tryptic digest and resulted in the ability to block low-mass, “background” ions which account for 40-70% of the total ion current from the ESI source during peak elution.