Introduction to Ion-selective Measurement

Product catalog summary

Theory of Ion-selective Electrodes (ISE): Ion-selective electrodes consist of an ion-specific half-cell and a reference half-cell. The potential difference between these cells depends on the ion concentration, described by the Nernst equation. Key constants include the universal gas constant (R) and Faraday constant (F). The slope (S) of the ISE is crucial for performance evaluation and maintenance.

Design of Ion-selective Electrodes: ISEs can be solid-state, PVC membrane, or gas-sensing electrodes. Solid-state electrodes use insoluble materials like Lanthanium fluoride for fluoride detection. PVC membrane electrodes involve polymerized materials reacting with specific ions. Gas-sensing electrodes detect ions through gas equilibrium, such as ammonium via ammonia detection.

Calibration and Measurement: Calibration involves preparing standard solutions and plotting concentration vs. potential. Two-point calibration is sufficient for specific concentration ranges, while multi-point calibration is necessary for non-linear ranges. Detection limits are determined graphically. Measurement requires stabilization and consistent mixing, with temperature control being critical.

Selectivity and Ionic Strength: ISEs may be sensitive to similar ions, affecting measurement accuracy. Selectivity constants help quantify this interference. Ionic strength adjustment (ISA) ensures sufficient ions for accurate measurement, often using ammonium salts.

Measurement Modes: Direct measurement requires a calibration curve, while incremental measurement accounts for matrix effects. Methods include standard addition and sample addition, calculated using specific equations.

Maintenance: Proper storage and conditioning of ISEs are essential to prevent contamination and damage. Cleaning should be gentle to avoid damaging the sensing surface.

Introduction to Ion-selective Measurement

Introduction to Ion-selective Measurement

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