CE-ESI Injection Assembly for Stable Nanoflow Electrospray
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Solution Overview
Problem
Existing CE-ESI-MS interfaces face challenges in achieving stable electrospray at nanoliter-per-minute flow rates and integrating optical detection capabilities, leading to limitations in sensitivity and analytical flexibility.
Innovation Solution
The proposed unitary optical-ESI system incorporates an injection subassembly with a nicked alignment tube and a spray needle, allowing for both sheath flow and sheathless ESI configurations, and integrates inline optical detection to enable orthogonal detection methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a porous capillary is used to provide electrical contact without introducing conducting liquid (sheathless interface), then sample dilution is eliminated and sensitivity is improved, but the porous tip becomes extremely fragile and deteriorates under high voltage leading to degraded electrospray
Solution Approach 1:
The interface is divided into two distinct parts: a robust separation capillary for electrophoresis and a separate spray emitter for electrospray ionization. The capillary outlet is inserted into the emitter without requiring the capillary itself to be porous or conductive, distributing the functional requirements to separate components that can each be optimized for their specific role.
Solution Approach 2:
A conducting liquid is introduced as an intermediary medium between the non-conductive separation capillary and the spray emitter. This conducting liquid provides the necessary electrical contact and electroosmotic flow generation at the emitter, while the capillary itself remains structurally simple and robust, eliminating the fragility issue of porous tips.
2Strength
If electrospray voltage is delivered directly to a metal needle (sheath flow interface), then the interface is more rugged, but bubble formation and corona discharge occur due to redox reaction on the metal surface limiting electrospray performance
Solution Approach 1:
The spray emitter is designed as a disposable or easily replaceable component with a non-metallic, non-reactive coating on its inner surface. This coating prevents redox reactions and bubble formation, and since the emitter is inexpensive and simple to replace, the system maintains high electrospray performance without the complications of metal needle degradation.
3Stability of the object's composition
If mechanical pump-driven flow is used to maintain stable electrospray in metal needle interface, then flow stability is achieved, but flow rate is higher than electrokinetically pumped interface leading to higher dilution and reduced sensitivity
Solution Approach 1:
The mechanical pump-driven flow system is replaced with an electrokinetically pumped interface using electroosmotic flow generated by applying voltage to the conducting liquid in the emitter. This eliminates the need for mechanical pumps, reduces flow rate to nanoliter-per-minute levels, and maintains electrospray stability through electrical control rather than mechanical pumping.
4Quantity of substance
If the separation capillary is made porous to enable sheathless ESI, then sample dilution is eliminated, but the etched capillary is extremely fragile and deteriorates under high voltage
Solution Approach 1:
The system separates the functions of sample delivery and electrospray generation into two distinct components: a robust separation capillary and a specialized spray emitter. The capillary remains non-porous and structurally simple, while the emitter handles the electrospray function, allowing each component to be optimized for its specific purpose without compromising the other.
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 solution achieves improved electrospray stability and sensitivity, enabling simultaneous ultraviolet and mass spectrometry detection, and provides flexibility in analytical configurations, overcoming the limitations of existing technologies.
Implementation Method 1
electroosmotic nanoflow to drive the electrospray
Implementation Method 2
electrospray ionization (ESI) in capillary electrophoresis with mass spectrometry
Data Source
AI summary
The disclosed solution comprises an injection subassembly that includes a nicked alignment tube, a spray needle, and a conducting liquid tube. The nicked alignment tube has a nick near one end. The spray needle is fused within the nicked end of the nicked alignment tube and the fused spray needle and nicked alignment tube are inserted into the conducting liquid tube, where the nicked alignment tube aligns the spray needle coaxially within the conducting liquid tube. The nick and the entry end of the spray needle are positioned within the conducting liquid tube and the exit end of the spray needle extends out of the conducting liquid tube. The nick allows a conducting liquid to flow from the conducting liquid tube to within the nicked alignment tube and the spray needle. Also disclosed are a unitary optical-ESI system equipped with the injection subassembly and a method for using the same.