Impactor Spray Ionization Source for CE-MS Polarity Switching
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Solution Overview
Problem
Conventional Capillary Electrophoresis (CE) mass spectrometry interfaces face challenges with rapid polarity switching due to the need for high voltage Electrospray ionization sources, which disrupt electroosmotic and electrophoretic flows and require additional power supplies, limiting buffer concentration and ESI voltage stability.
Innovation Solution
A grounded tri-axial pneumatic nebuliser probe is used to decouple ionizing high voltage from the probe tip, allowing fast polarity switching of an impactor target for single CE/MS runs, eliminating the need for high voltage power supplies and stabilizing the CE voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high voltage Electrospray ionization source is used to interface CE with mass spectrometry, then ionization efficiency is improved, but the ability to rapidly switch polarity is compromised due to disruption of electroosmotic and electrophoretic flows
Solution Approach 1:
The system separates the ionization function from the CE separation function by using two independent voltage control paths: one for the CE column (maintaining stable electroosmotic flow) and one for the impactor target (enabling rapid polarity switching for ionization). This segmentation allows both functions to operate optimally without interfering with each other.
Solution Approach 2:
The impactor target acts as an intermediary component between the CE column outlet and the mass spectrometer. It receives the neutral eluent from the CE column and provides the high voltage for ionization, thereby decoupling the voltage requirements of the CE separation system from the ionization system and enabling independent polarity switching.
2Reliability
If the Electrospray probe tip is biased to high voltage for ionization, then ionization efficiency is improved, but additional power supply circuits and increased system complexity are required
Solution Approach 1:
The high voltage bias is extracted from the probe tip structure and relocated to a separate impactor target. This removes the need for complex high voltage power supply circuits integrated into the probe assembly, simplifying the overall system architecture while maintaining effective ionization capability.
Solution Approach 2:
The ionization function is moved from the spatial dimension of the probe tip to a separate dimensional location (the impactor target positioned downstream). This spatial separation allows the probe tip to remain simple and grounded while the ionization function is performed at a different location with dedicated voltage control.
3Reliability
If the Electrospray probe tip is biased to high voltage, then ionization is enhanced, but ESI voltage stability and buffer concentration limitations are imposed
Solution Approach 1:
The voltage control is segmented into two independent systems: the CE column voltage (which determines electroosmotic flow and must remain stable) and the impactor target voltage (which provides ionization and can be rapidly switched). This segmentation eliminates the coupling between voltage stability requirements and polarity switching requirements, allowing each to be optimized independently.
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
Enables efficient analysis of both positive and negative ions in a single CE/MS run with improved stability and reduced costs by maintaining the probe at ground potential and using a grounded probe assembly, enhancing the interfacing of CE with mass spectrometry.
Implementation Method 1
A flow of make-up solution is added to the second concentric capillary which mixes with the flow from the inner capillary at the probe tip. The resulting liquid stream is converted into a nebulised spray via a concentric flow of high velocity gas from a third concentric capillary.
Implementation Method 2
A small impactor target is preferably positioned in relatively close proximity to the nebuliser tip to define an impact zone and to ionize the incoming high velocity droplet stream.
Implementation Method 3
Analytes elute from the column at a rate that is determined by a combination of electroosmotic flow and the electrophoretic mobility of the analytes
Implementation Method 4
Capillary Electrophoresis (CE) is a separation technique where a high voltage is applied to the sample inlet end of a glass capillary column
Data Source
Figure 1~2(b)
AI summary
A mass spectrometer is disclosed comprising a separation device arranged and adapted to emit an eluent over a period of time. The separation device preferably comprises a Capillary Electrophoresis ("CE") separation device. The mass spectrometer further comprises a nebuliser (2) and a target (11). Eluent emitted by the separation device is nebulised, in use, by the nebuliser wherein a stream of analyte droplets are directed to impact upon the target (11) so as to ionise the analyte to form a plurality of analyte ions.