pH Sensor Redox Electrode Selective Layer
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Solution Overview
Problem
Electrochemical sensors face challenges in accurately measuring pH in unbuffered or low-buffer-concentration aqueous solutions, leading to anomalous pH readings due to difficulties in proton transfer reactions.
Innovation Solution
The use of an electrode with a redox active compound covered by a selective layer that allows the passage of hydrogen ions but not other atoms, enabling accurate pH determination in both buffered and unbuffered solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a redox active compound is used for pH measurement, then pH determination is enabled through redox potential monitoring, but measurement accuracy deteriorates in unbuffered or low-buffer-concentration solutions due to failed proton transfer reactions
Solution Approach 1:
A selective covering layer is introduced as an intermediary between the redox active compound and the aqueous solution. This layer mediates proton transfer reactions by selectively allowing hydrogen ions to pass through while blocking other atoms, thereby enabling reliable pH measurements in unbuffered or low-buffer-concentration solutions where direct proton transfer would otherwise fail
Solution Approach 2:
The covering layer is applied locally over the redox active compound to create a specialized interface region. This local modification provides selective proton transfer capability exactly where needed at the electrode-solution interface, without altering the bulk properties of the solution or the redox compound itself
2Reliability
If a selective covering layer is added to enable proton transfer, then measurement reliability in unbuffered solutions is improved, but device complexity increases
Solution Approach 1:
The covering layer is implemented as a thin film structure that selectively permits hydrogen ion passage while blocking other atoms. This thin film approach achieves the desired selectivity and reliability improvement without adding significant structural complexity, bulk volume, or operational complexity to the sensor device
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 enhances the accuracy of pH measurements in aqueous liquids with low buffer concentrations, reducing anomalous readings and improving the reliability of pH determination across various solution conditions.
Implementation Method 1
at least one redox active compound on the substrate which is able, in contact with aqueous liquid, to undergo a redox reaction involving both electron and proton transfer
Implementation Method 2
a covering layer over the redox active compound wherein the covering layer selectively allows the passage of hydrogen ions but not other atoms to the redox active compound
Data Source
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AI summary
A method of determining the pH of an aqueous liquid which contains little or no buffer, such as does not contain more than 0.01 moles per litre of pH-buffering partially dissociated acid, base and/or salt, uses an electrode with at least one redox active compound immobilized thereon convertible electrochemically between reduced and oxidized forms with transfer of at least one proton between the compound and the aqueous liquid. Varying potential is applied to the electrode, observing current flow as potential is varied, determining the applied potential at a maximum current for redox reaction of the compound, and determining pH from the potential at maximum current. The electrode has a covering layer which separates the redox active compound from the aqueous liquid but selectively allows the passage of hydrogen ions between the redox active compound and the aqueous liquid. The presence of the covering layer enhances accuracy of the measurement of pH of the aqueous liquid.