Electrospray Current Sensing Circuit for Nanoamp Leakage Isolation
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Solution Overview
Problem
Measuring small ion currents in nanospray and microspray regimes of electrospray ionization is challenging due to high common mode voltage and leakage currents, requiring precise current measurement to nanoamps resolution while avoiding damage to downstream electronics.
Innovation Solution
A high-side current sensing circuit is configured to directly measure electrospray current using a current sensing resistor, isolating the desired spray current from stray and leakage currents, and optionally utilizing an isolation amplifier to protect downstream electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high voltage is applied to create charged droplets for electrospray ionization, then ionization efficiency is improved, but current leakage and common mode voltage increase making measurement difficult
Solution Approach 1:
The system segments the current measurement by using a current sensing resistor to measure only the spray current component, separating it from the total current that includes leakage. The high voltage is applied selectively to the electrospray emitter rather than the entire fluid path, isolating the ionization function from the measurement path.
Solution Approach 2:
A current sensing resistor is introduced as an intermediary element between the power source and the electrospray emitter. This resistor enables precise measurement of the spray current by converting it to a measurable voltage signal, while the high voltage is applied through a separate path that does not interfere with the measurement circuit.
2Measurement precision
If high voltage is applied to the fluid union to ionize the sample, then ionization efficiency improves, but current leakage from the fluid union increases
Solution Approach 1:
The electrical circuit is segmented into two separate paths: one path applies high voltage to the electrospray emitter for ionization, while the other path measures current through the current sensing resistor. The fluid union is electrically isolated from the measurement circuit, so leakage currents at the fluid union do not contaminate the spray current measurement.
Solution Approach 2:
The measurement of spray current is extracted from the total current path by placing the current sensing resistor in series with the electrospray emitter only. This separates the measurement function from the fluid handling components, eliminating interference from leakage currents that occur at the fluid union and column interfaces.
3Measurement precision
If conventional current measurement methods are used, then system complexity is reduced, but measurement resolution cannot achieve nanoamps precision
Solution Approach 1:
The system replaces complex electromagnetic measurement methods with a simple ohmic measurement approach. By using a current sensing resistor and measuring the voltage drop across it, the system achieves nanoamp resolution through basic Ohm's law calculation, avoiding the need for complex current transformers or electromagnetic sensors.
Solution Approach 2:
The measurement approach changes from measuring current directly to measuring voltage across a known resistance. This parameter transformation allows the use of high-precision voltage measurement circuits to achieve nanoamp current resolution, leveraging the higher precision typically available in voltage measurement technology.
4Reliability
If high voltage is applied to multiple ports including fluid reservoir, then ionization coverage is improved, but current leakage toward the reservoir increases
Solution Approach 1:
The electrical isolation segments the high voltage application to only the electrospray emitter port, while the fluid reservoir and column ports remain at ground potential. This segmentation ensures that ionization occurs reliably at the emitter without creating leakage current paths toward the reservoir, as the electrical potential difference is confined to the emitter only.
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 allows for accurate and precise measurement of electrospray current, enabling characterization and optimization of the electrospray apparatus, and diagnosing cartridge health without complex imaging algorithms, with improved fidelity and automation capabilities.
Implementation Method 1
a power source coupled with the fluid union and configured to apply a voltage potential to the fluid union sufficient to ionize the fluid sample to form an ionized fluid sample
Implementation Method 2
the current sensing circuit can include a current sensing resistor
Data Source
AI summary
An electrospray ionization system used in mass spectrometry provides for improved current measurement. The system includes a fluid union, a fluid column coupled with a first port of the fluid union, a power source coupled with the fluid union and configured to apply a voltage potential to the fluid union, and an electrospray emitter coupled with a second port of the fluid union. The power source is coupled with the first port and configured to apply the voltage potential to the first port to restrict current leakage from the fluid union. The current sensing circuit is configured to determine an electrical current flow between the power source and the at least one of the fluid union and the first port.