Electrokinetically Pumped ESI-MS Interface for Stable Negative Ion Analysis

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Solution Overview

Problem

Current electrospray ionization interfaces for capillary electrophoresis-mass spectrometry face challenges in maintaining stable electrospray in negative ion mode, leading to inefficient analysis of analytes due to reverse electro-osmotic flow and instability.

Innovation Solution

A glass emitter with a surface coating of organic chemicals, such as aminopropyltrimethoxysilane, is used to reverse electroosmosis, ensuring stable electroosmotic flow towards the emitter orifice even under negative electrospray voltage, thereby stabilizing the electrospray and improving analysis efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If negative potential is applied to the emitter for negative-ion electrospray, then the electrospray can analyze certain analytes, but the electro-osmotic flow is directed away from the emitter orifice causing unstable spray

Engineering Contradiction:

Improvecapability to analyze analytes in negative-ion modeVSAvoidstability of electrospray

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The invention inverts the surface charge of the emitter by applying a positive charge coating to the interior surface. This reverses the direction of electro-osmotic flow from away-from-orifice to toward-orifice, enabling stable negative-ion electrospray. The coating material (e.g., aminopropyltrimethoxysilane) provides permanent positive charge that counteracts the negative potential applied during operation.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention changes the surface charge parameter of the emitter from negative (natural glass surface) to positive (coated surface). This parameter change fundamentally alters the electro-osmotic flow direction, allowing the system to maintain stable flow toward the orifice even when negative potential is applied for negative-ion analysis.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If untreated glass emitter is used with negative potential, then negative-ion electrospray can be generated, but flow is directed away from the emitter orifice producing unstable electrospray

Engineering Contradiction:

Improveability to perform negative-ion mode analysisVSAvoidstability and efficiency of spray

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If sheath liquid flow rate is increased to support electrospray, then electrical connection is maintained, but high dilution of analyte occurs

Engineering Contradiction:

Improveelectrical connection stabilityVSAvoidanalyte concentration

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The invention replaces the mechanical pump system with an electro-kinetically driven system. The electro-osmotic flow generated by the charged surface provides precise, low-rate liquid transport without the high flow rates and associated dilution problems of mechanically pumped systems. This substitution maintains electrical connection while preserving analyte concentration.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 stable and sensitive analysis of analytes across three orders of magnitude with limits of detection as low as 150 to 900 attomoles, significantly improving the performance of negative mode electrospray ionization-mass spectrometry by maintaining a stable electrospray and reducing variability.

Implementation Method 1

application of an electric field generates electroosmotic flow at the interior of a glass emitter... This electroosmotic flow pumps sheath liquid around the distal tip of the separation capillary

Methodology Applied

Scientific EffectElectroosmosis: Electro-Osmosis

Implementation Method 2

positive charges formed on the functional moieties stabilize the direction of the EOF in negative mode

Methodology Applied

Scientific EffectElectroosmotic flow: Electro-Osmotic Flow

Data Source

PatentUS11056329B2ESI-MS via an electrokinetically pumped interface

Publication Date: 2021.07.06 UNIV OF NOTRE DAME DU LAC

AI summary

An electrokinetically pumped sheath flow nanospray interface for capillary electrophoresis coupled to negative mode electrospray mass spectrometer is described. At this interface, application of an electric field generates electro-osmotic flow at the interior of a glass emitter having an orifice. Electroosmotic flow pumps liquid around the distal tip of the separation capillary, ensheathing analyte into the electrospray electrolyte. In negative ion mode, negative potential applied to an untreated emitter drives sheath flow away from the emitter orifice, decreasing the stability and efficiency of the spray. In contrast, when the interior of the electrospray emitter is grafted with aminoalkylsilanes, the amines have a positive charge, which reverses electroosmosis and generates stable sheath flow to the emitter orifice under negative potential. Limits of detection were about 150 to 900 attomoles injected. Negative mode operation was demonstrated by analyzing a metabolite extract from stage 1 Xenopus laevis embryos.