RF Multipole Rod System for Simultaneous Ion Storage
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Solution Overview
Problem
Conventional RF multipole rod systems have limitations in storing ions across a wide mass range, particularly failing to simultaneously retain light ions like electrons and heavy positive ions due to upper and lower mass limits, which restricts their application in mass spectrometry, especially in peptide analysis and reaction studies.
Innovation Solution
An RF multipole rod system with at least eight pole rods, utilizing two independent RF voltages to generate separate or superimposed multipole fields of different orders, allowing for the radial storage of low-energy electrons and heavy positive ions, enabling reactions such as electron capture dissociation and electron transfer dissociation, and facilitating the formation of a fine ion beam for analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional RF multipole rod system is used, then ions within a specific mass range can be stored, but ions outside this mass range (particularly light ions like electrons and heavy positive ions) cannot be simultaneously retained
Solution Approach 1:
The multipole rod system is divided into multiple independent rod groups, each capable of generating a separate multipole field of different order. This segmentation allows different mass ranges to be handled by different rod groups simultaneously, enabling both light ions (electrons) and heavy positive ions to be stored in the same device without interfering with each other.
Solution Approach 2:
The rod system is designed to perform multiple functions: it can store light ions (electrons) in one multipole field while simultaneously storing heavy positive ions in another multipole field. The same physical structure serves multiple purposes by generating different field configurations in different spatial regions, achieving universality in ion storage across wide mass ranges.
2Adaptability or versatility
If a single multipole field is used in the rod system, then the structure remains simple, but the ability to store ions of different masses simultaneously is lost
Solution Approach 1:
The control system is segmented to independently control different rod groups. Each rod group has its own control electrodes and power supplies, allowing independent generation of different multipole fields. This segmented control architecture enables complex simultaneous field configurations without requiring a completely redesigned monolithic control system.
Solution Approach 2:
Multiple multipole fields of different orders are merged within the same physical rod system. The fields are superimposed in space but remain independently controllable through the segmented rod groups. This merging approach allows the system to achieve the functionality of multiple devices while using a single integrated structure.
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 configuration enables the simultaneous storage and reaction of ions across a wide mass range, enhancing the detection of heavy ions and improving the resolution in mass spectrometry by allowing the formation of a fine ion beam, overcoming the limitations of conventional systems.
Implementation Method 1
The effect of the multipole systems is described by so-called 'pseudopotentials', fictitious potentials which make it possible to describe the effect of inhomogeneous alternating fields on ions in a simple way.
Implementation Method 2
An alternating field at the tip of a wire, whose strength decreases at 1/r2, or an alternating field around a long wire, which decreases at 1/r, reflects both positively and negatively charged particles.
Implementation Method 3
If a rod system such as this is filled with a collision gas at a pressure between 0.01 and 1 pascal, ions injected with a few electronvolts give up most of their kinetic energy as a result of collisions with this gas in a short period of time of only 0.1 to 10 milliseconds and collect as a thin string of ions only with thermal energy in this potential well along the axis.
Implementation Method 4
This focusing effect can also be observed when the ions are transported through a gas-filled multipole system. This process, described already in German Patent DE 27 01 395, is now called 'collision focusing'.
Data Source
AI summary
The invention relates to devices and methods for the storage of ions in mass spectrometers. The invention proposes the generation and superposition of two multipole fields of different order, independent of each other, in an RF multipole rod system. In an embodiment with eight pole rods, for example, it is thus possible to jointly store low-energy electrons in a central RF quadrupole field, which effectively acts only on electrons and holds them together radially, on the one hand, and multiply charged heavy positive ions in an RF octopole field, which effectively acts only on the ions, on the other hand, in order to fragment the positive ions by electron capture dissociation (ECD). In a different embodiment, multiply charged positive analyte ions and suitable negative reactant ions can react with each other in an octopole field by electron transfer dissociation (ETD) with a high fragmentation yield, and the fragment ions can subsequently be bundled by a transition to a quadrupole field to form a fine ion beam, which can leave the multipole rod system axially. A mixture of hexapole and dodecapole systems is also possible.