Voltammetric pH Sensor with Hydrogen Bonding Substituents
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Solution Overview
Problem
Electrochemical sensors face challenges in accurately measuring pH in unbuffered aqueous solutions due to difficulties in electrochemical measurements without a buffer or facilitating species for proton transfer, leading to erroneous results, especially in low ionic strength media like rainwater and natural waters with minimal mineralization.
Innovation Solution
The use of redox active compounds with specific substituents that enhance proton transfer rates by promoting hydrogen bonding, such as oxygen or nitrogen-containing groups, which are immobilized on electrodes, facilitating concerted electron-proton transfer processes, allowing for accurate pH measurement in unbuffered solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional electrochemical sensors with immobilized redox compounds are used in unbuffered aqueous solutions, then the sensor structure is simple and does not require buffer addition, but the measurement accuracy deteriorates due to depletion of H+ ion concentration near the electrode
Solution Approach 1:
The patent modifies the chemical parameters of the redox compound by introducing specific substituent groups (oxygen-containing or nitrogen-containing groups) that enhance proton transfer capability. This changes the kinetic parameters of the electrochemical reaction, enabling fast proton transfer that prevents local pH changes near the electrode surface, thereby maintaining measurement accuracy in unbuffered solutions.
Solution Approach 2:
The substituent groups on the redox compound act as intermediaries that facilitate proton transfer between the solution and the electrode. These groups (such as hydroxyl, carbonyl, or amino groups) serve as proton relay stations, enabling efficient proton exchange without requiring buffer species in the bulk solution, thus resolving the contradiction between simplicity and accuracy.
2Device complexity
If redox compounds without proton transfer facilitating groups are used, then the sensor design is simpler, but the reaction rate of proton transfer decreases leading to erroneous pH determination
Solution Approach 1:
The patent systematically modifies molecular parameters by incorporating substituent groups with specific chemical properties (oxygen or nitrogen atoms) that increase the reaction rate constant for proton transfer. This parameter change transforms the kinetic behavior of the redox compound, enabling it to facilitate rapid proton exchange without significantly complicating the overall molecular structure.
3Reliability
If measurements are performed in low ionic strength media without buffers, then the sample composition remains natural and unaltered, but the electrochemical measurements become error-prone due to insufficient proton transfer facilitation
Solution Approach 1:
The redox compound with substituent groups serves as an intermediary that enables reliable electrochemical measurements in natural, unbuffered samples. The substituent groups mediate proton transfer reactions at the electrode surface, ensuring accurate pH determination without requiring addition of buffer substances that would alter the natural composition of the sample.
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 reliable pH determination in unbuffered aqueous solutions by reducing activation energy for proton transfer, ensuring accurate measurements comparable to those in buffered solutions, even in low ionic strength media.
Implementation Method 1
a redox active compound, which may be an organic compound, convertible electrochemically between reduced and oxidized forms
Implementation Method 2
a group containing oxygen or nitrogen and positioned to participate in hydrogen bonding with a water molecule also able to hydrogen bond to the redox active functional group
Implementation Method 3
measuring potential or potentials corresponding to one or more said oxidation and/or reductions; and processing the measurements to give a determination of pH
Data Source
AI summary
A voltammetric pH sensor, especially for characterising wellbore fluids, comprises a plurality of electrodes with a redox active organic compound attached to an electrode and having at least one functional group convertible electrochemically between reduced and oxidized forms with transfer of at least one proton between the compound and surrounding aqueous phase, wherein the compound has at least one substituent group which promotes hydrogen bonding at a said functional group and thereby increases the reaction rate of proton transfer. The substituent group may form an internal hydrogen bond with a redox-convertible group or may enhance polarity to promote electrostatic interaction with water molecules and reduce activation energy. Typical examples include alizarin or 1, 2 - dihydroxy- anthraquinone (RH=72 - 48 - 0 ), quinizarin or 1, 4 - dihydroxy- anthraquinone (RN=81 - 64 - 1), 2 - acetoxy-benzoquinone (RN=1125 - 55 - 9 ), chloranil or 2, 3, 4, 5 - tetrachloro -benzoquinone (RN=118 - 75 - 2 ) and 1, 4 - diamino - 2, 3 - dichloro - anthraquinone (RN=81 - 42 - 5 ) deposited on a glassy carbon electrode. In this way, anomalous measurements at low ionic strenght and low concentrations of pH buffering species can be overcome.