Ion-Selective Electrode Waveform Segmentation for Calcium Measurement
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Solution Overview
Problem
Existing methods for measuring calcium ion concentrations using polymer-based ion-selective electrodes (ISEs) suffer from inaccuracies due to sensor drift, which is corrected by normalizing electrical potential measurements, leading to signal corruption and inaccurate calcium level recordings.
Innovation Solution
A method involving a waveform analysis that separately models calibration and sampling portions of electrical potential measurements, using diffusion and drift models to normalize the electrical potential difference, thereby accounting for sensor drift without distorting the signal morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrical potential measurements are normalized to correct for sensor drift, then measurement accuracy is improved, but signal morphology is corrupted leading to inaccurate calcium level recordings
Solution Approach 1:
The waveform is divided into distinct segments: calibration portion and sampling portion. By separating these portions, the patent applies different processing approaches to each - drift correction is applied to the calibration portion while the sampling portion preserves its original morphology for accurate calcium level determination.
Solution Approach 2:
The drift component is extracted and removed from the calibration portion of the signal. This allows the drift artifact to be corrected independently without affecting the morphology of the sampling portion, thereby resolving the contradiction between drift correction and signal preservation.
2Reliability
If drift component is removed from electrical potential signal to account for sensor drift, then calibration accuracy is improved, but signal morphology is corrupted
Solution Approach 1:
The signal is segmented into calibration and sampling portions. Drift removal is applied only to the calibration portion to improve calibration accuracy, while the sampling portion retains its original morphology for reliable calcium level measurement.
Solution Approach 2:
Drift correction is performed as a preliminary step on the calibration portion before proceeding to analyze the sampling portion. This preliminary action improves calibration accuracy without compromising the integrity of the subsequent measurement phase.
3Duration of action of moving object
If sensor measurements are used beyond initial calibration period, then extended monitoring is achieved, but measurement accuracy decreases due to sensor drift and gradual failures
Solution Approach 1:
The system performs periodic recalibration by alternating between calibration fluid and unknown fluid measurements. This periodic recalibration compensates for sensor drift over time, extending the operational longevity of the sensor while maintaining measurement accuracy through repeated normalization cycles.
Solution Approach 2:
The system uses feedback from the calibration measurements to detect and correct drift in real-time. By continuously monitoring the calibration signal and adjusting subsequent measurements accordingly, the system maintains accuracy over extended operational periods despite sensor aging and drift.
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 provides accurate and consistent ion concentration measurements, enhances sensor longevity, and improves measurement accuracy by incorporating sensor sensitivity into the calculation, reducing errors from drift and gradual failures.
Implementation Method 1
ISEs work on the principle of selective ion binding, where a membrane in the electrode selectively allows only a specific ion-i.e., a calcium ion (Ca2+)-within a fluid sample to pass through and thereby generate an electrical potential
Implementation Method 2
The electrical potential is read by a measuring instrument and is subsequently converted into a calcium ion concentration value (e.g., using a suitable Nernst equation)
Implementation Method 3
The diffusion of the measurements during the transition from measuring the calibration fluid to measuring the unknown fluid is modelled using a first model
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A device for measuring ion concentration in fluid samples comprises a sensor assembly to obtain voltage measurements from a fluid sample and a control unit with processors configured to obtain a signal from the sensor assembly with a calibration portion and a sampling portion. A first model is fit to the sampling portion to identify a first time point with a settled voltage value. A second model is fit to the calibration portion to identify a calibration voltage value at the first time point. The voltage difference between the sampling portion's voltage at the first time point and the calibration voltage value is determined and the voltage difference is shifted by an amount corresponding to the difference between the calibration voltage value and a predetermined voltage value. The ion concentration of the unknown fluid is calculated based on the normalized voltage difference.