Construction and working of Standard hydrogen electrode
The standard hydrogen electrode (SHE) is a reference electrode used in potentiometry analysis. It consists of a platinum electrode immersed in a solution of 1 M HCl and surrounded by a gaseous atmosphere of hydrogen at a pressure of 1 bar.
Construction of the Standard Hydrogen Electrode:
The construction of the SHE involves a few steps:
- Take a platinum wire, and clean it using a suitable solvent, such as acetone or ethanol, to remove any impurities.
- Dip the cleaned platinum wire into a solution of hydrochloric acid (HCl), which acts as an electrolyte.
- Install the platinum wire in a glass tube and seal the tube using a stopper.
- The glass tube is then connected to a hydrogen gas supply through a side arm. The hydrogen gas should be dry and free from impurities.
- The hydrogen gas is bubbled through the solution of HCl, and a platinum black coating is formed on the surface of the platinum wire.
Working of SHE
- The SHE is immersed in the solution being analyzed, along with an indicator electrode.
- The hydrogen gas surrounding the platinum electrode is allowed to diffuse into the solution, and hydrogen ions (H+) are formed at the surface of the platinum black coating.
Pt(s) + 2H+(aq) ⇌ Pt2+(aq) + H2(g)
- The potential difference between the SHE and the indicator electrode is measured using a high-impedance voltmeter or a potentiometer.
- The measured potential difference is used as a reference point to measure the potential difference between the indicator electrode and the solution being analyzed.
- The potential difference between the SHE and the indicator electrode is taken as zero, and the potential difference between the indicator electrode and the solution being analyzed is measured to calculate the concentration of the analyte in the solution.
The SHE is a stable and reproducible reference electrode, and its potential is defined as zero at standard conditions (25°C, 1 atm pressure, and a 1 M H+ concentration). The SHE is used as a reference electrode in many electrochemical measurements and is essential for the calibration of potentiometric sensors.
Applications
1. Electrochemical Impurity Analysis:
Electrochemical methods, such as cyclic voltammetry and potentiostatic/galvanostatic techniques, can be used to analyze impurities in pharmaceutical compounds. By comparing the electrochemical behavior of a substance with that of known standards using a reference electrode like SHE, researchers can identify and quantify impurities in drug formulations.
2. Determination of Redox Potential:
Electrochemical redox potentials play a crucial role in understanding the stability and reactivity of pharmaceutical compounds. Using the SHE as a reference electrode, researchers can measure and calculate redox potentials of drugs and their intermediates. This information aids in predicting the compound’s stability and potential interactions with other substances.
3. Electrochemical Sensors and Biosensors:
Electrochemical sensors and biosensors are used in pharmaceutical analysis for detecting various analytes, including drugs and metabolites. The reference electrode helps establish a stable potential difference, enabling accurate and sensitive measurements of electrochemical signals produced by interactions between analytes and sensor surfaces.
4. Antioxidant Activity Testing:
Pharmaceutical compounds with antioxidant properties can be evaluated using electrochemical methods. The SHE can be part of a setup to measure the ability of a drug to scavenge reactive oxygen species and assess its potential as an antioxidant.
5. Electrochemical Characterization of Pharmaceutical Polymers:
Polymeric materials are widely used in pharmaceutical formulations. Electrochemical techniques, combined with reference electrodes, can characterize the electrochemical properties of polymers used in drug delivery systems, coatings, or packaging.
6. Development of Electrochemical Assays:
Electrochemical assays are employed for analyzing pharmaceutical compounds, including those used for quality control or determining the concentration of active ingredients. The SHE is integral to establishing the potential difference required for accurate assay measurements.
7. Understanding Electrochemical Interactions:
Electrochemical interactions between drugs and biological molecules, such as proteins or DNA, can be studied to gain insights into drug-target interactions and potential toxicity. Reference electrodes aid in maintaining stable electrode potentials during these investigations.
In summary, while the direct application of the Standard Hydrogen Electrode itself might be limited in pharmaceuticals, the underlying electrochemical principles and related techniques have diverse applications. These applications contribute to drug development, analysis, stability assessment, and the understanding of pharmaceutical compounds’ behavior in various contexts.
Frequently Asked Questions (FAQs) on Standard Hydrogen Electrode (SHE)
The Standard Hydrogen Electrode (SHE) is a reference electrode used in electrochemistry to measure and standardize electrode potentials. It consists of a platinum electrode immersed in a solution of 1 Molar hydrogen ion (H⁺) at a pressure of 1 atmosphere, with hydrogen gas bubbling over the surface.
The SHE is used as a reference electrode because its electrode potential is defined as zero volts at all temperatures. This makes it an ideal reference point for comparing the electrode potentials of other half-cells and measuring their relative values.
The potential of the SHE is arbitrarily set as zero volts at all temperatures. This means that any other electrode potential is measured relative to the SHE’s potential.
The SHE is set up by immersing a platinum electrode in a solution containing 1 Molar H⁺ ions at 1 atmosphere pressure. Hydrogen gas is bubbled over the platinum electrode. The electrode potential of this setup is taken as the reference point.
Platinum is used because it does not react with most substances and is inert in many electrolytes. This ensures that the electrode potential is not affected by reactions occurring at the electrode surface.
The SHE is not practical for many experimental setups due to its complexity and the need to maintain constant 1 atm pressure of H₂ gas. It is mainly used as a theoretical reference point.
The Nernst equation relates the electrode potential of a half-cell to the concentration of ions in the solution. The potential of the SHE at 1 Molar H⁺ concentration is used as a reference in the Nernst equation to calculate electrode potentials for other half-cells.
The SHE is used in various electrochemical studies, including the determination of standard electrode potentials, calculation of cell potentials, and the measurement of equilibrium constants for redox reactions.
While the SHE is typically set up in a solution with 1 Molar H⁺ ions, it can also be used as a reference electrode in other solutions. Adjustments to the Nernst equation are made when working in solutions with different H⁺ ion concentrations.
Yes, there are alternative reference electrodes like the Ag/AgCl electrode, the Calomel electrode (Hg/Hg₂Cl₂), and the Saturated Calomel Electrode (SCE), which are more practical for various experimental setups.
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