Ion Mobility Measurement Using Dual Quadrupole Mass Filters
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Solution Overview
Problem
Current methods for measuring ion mobility in mass spectrometry struggle to distinguish between isomeric ions of the same mass but different folding structures, as they cannot effectively filter out fragment ions or differentiate between isomers and fragment ions, leading to incomplete analysis of ion mixtures.
Innovation Solution
A method involving a first mass filter for selecting ions by mass, followed by a mobility measurement in a drift region with a collision gas under an electric field, and a second mass filter to remove unwanted ions, with quadrupole mass filters and ion guides used to maintain pressure differentials and focus ions, allowing for time-resolved detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single mass filter is used to select ions by mass, then ions of the same mass are selected, but fragment ions cannot be distinguished from intact isomers
Solution Approach 1:
The patent divides the ion analysis process into two distinct mass filtering stages: a first mass filter before the mobility measurement to select parent ions, and a second mass filter after the mobility measurement to analyze fragment ions. This segmentation allows the system to separately identify and characterize both intact isomers and fragment ions, resolving the information loss problem while maintaining measurement precision.
2Ease of operation
If ion mobility measurement is performed without post-mobility mass filtering, then measurement simplicity is maintained, but fragment ions contaminate the mobility signal
Solution Approach 1:
The patent applies preliminary action by performing the first mass filter selection before the mobility measurement to ensure only intact parent ions enter the drift region. This preliminary filtering prevents fragment ions from contaminating the mobility signal, thereby maintaining both measurement simplicity and signal purity simultaneously.
Solution Approach 2:
The patent extracts fragment ions from the mobility measurement process by introducing a second mass filter after the drift region. This allows the system to separate and analyze fragment ions distinct from the mobility measurement of intact ions, thereby purifying the mobility signal while maintaining operational simplicity through automated sequential filtering.
3Measurement precision
If the drift region pressure is increased to enhance ion mobility measurement sensitivity, then measurement precision improves, but ion guides cannot maintain pressure differentials
Solution Approach 1:
The patent introduces gas-permeable ion guides as intermediary components between the drift region and the mass filters. These ion guides act as pressure buffers that can withstand the high pressure in the drift region while maintaining the vacuum necessary in the mass filter chambers. This intermediary structure allows the system to simultaneously achieve high measurement precision through enhanced drift region pressure and proper pressure differential maintenance through the ion guide's pressure-buffering capability.
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 enables the separation and identification of isomeric ions based on mobility, improving the distinction between intact isomers and fragment ions, and providing a more comprehensive analysis of ion mixtures by enhancing the dynamic range of measurement.
Implementation Method 1
a first mass filter for selecting ions by mass
Implementation Method 2
The high number of collisions with the gas molecules results in a constant drift velocity for each ionic species, which is proportional to the electric field intensity
Implementation Method 3
The ions of the substance under investigation are pulled through the gas by means of an electric field
Implementation Method 4
removing ions of unwanted masses in a second mass filter
Data Source
AI summary
The mobility of mass-selected ions in gases is measured at pressures of a few hectopascal by selecting the ions under investigation in a quadrupole filter according to their mass-to-charge ratio m/z, measuring their mobility in a drift region at a pressure of a few hundred Pascal under the influence of a DC electric field and then filtering the measured ions by means of a quadrupole field in order to eliminate, or detect changes in, the mass-to-charge ratio. Several embodiments for the drift region are disclosed, in which the ions are kept in the axis of the drift region by RF fields. As these drift regions can also be utilized for a collision-induced decomposition of the ions, the device can additionally be used as a so-called triple quadrupole mass spectrometer.