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Voltammetry: A Look at Theory and Application

Voltammetry: A Look at Theory and Application. Bobby Diltz 14 March 2005. Analytical Methods. Chromatography Large amounts of materials used Not very sensitive Spectroscopy Very sensitive Able to separate species Voltammetry Extremely sensitive Few components used

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Voltammetry: A Look at Theory and Application

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  1. Voltammetry: A Look at Theory and Application Bobby Diltz 14 March 2005

  2. Analytical Methods • Chromatography • Large amounts of materials used • Not very sensitive • Spectroscopy • Very sensitive • Able to separate species • Voltammetry • Extremely sensitive • Few components used • Wide range of concentrations

  3. What is Voltammetry? • As an applied potential is changed over time a current is measured • Reduces ions in the electrode • Commonly uses three electrodes • Working Electrode (WE) • Auxiliary Electrode (AE) • Reference Electrode (RE)

  4. Applications • Ultra Trace range metals (sub ppb) • Wastewater Analysis • Industrial Water/Liquor Analysis • “Polarographic Determination of Sulfur Compounds in Pulping Liquors” Dr. J.J. Renard • Sulfur compounds in weapons • Pharmaceutics • Environmental Studies • Biological/Biochemical Analysis • Plating Analysis

  5. Techniques • Polarography • Uses direct reduction at the electrode • This technique has limited sensitivity • Uses the mercury drop electrode (SDME, DME) • Voltammetry (Anodic Stripping/Adsorptive Cathodic Stripping) • Electrochemical deposition • Determination by stripping • Very high sensitivity, down to the parts per trillion range • Uses a stationary electrode (HDME, RDE)

  6. Working Electrode • The working electrode is used to show the response of the analyte to the potential • Mercury Electrode • Hanging Drop Mercury Electrode (HDME) • Used in the ppb to low ppm range • Static Drop Mercury Electrode (SDME) • Used in the low ppm range • Dropping Mercury Electrode (DME) • Used in the ppm range

  7. Working Electrode (cont) • Rotating Disk Electrode (RDE) • Ultra Trace Graphite • Gold • Glassy Carbon* • Many other types of WE

  8. Auxiliary Electrode • Completes the circuit between the potentiostat and the WE • Two different types available • Platinum • Glassy Carbon

  9. Reference Electrode • Provides a reference potential to the WE/AE circuit • Two types of RE • Ag/AgCl in KCl • Hg/HgCl in saturated KCl

  10. Electrolyte • One of the most difficult parts of method development with voltammetry!! • Electrolyte selection is greatly based on type of matrix • Electrolytes reduce voltage drop and promote a better flow of electrons through the solution, while also stabilizing half-wave potentials of analytes • Adjusts the pH • Increases selectivity

  11. Measurement Modes • Direct Current • Sensitivity of 10-5 mol/L • Low separation ability • Wave form of polarogram • Differential Pulse • Sensitivity of 10-8 mol/L • High separation • Peak form of polarogram

  12. More Measurement Modes • Alternating Current • Only for reversible reactions • Square Wave • Better for reversible reactions • Fast determinations • Cyclic Voltammetry • Useful in kinetic studies/qualitative analysis • Uses both oxidation and reduction steps

  13. Why Use Voltammetry? • Handles high salt concentrations better than chromatographic instrumentation • Can differentiate between ionic species • Example: Cr6+  Cr3+ • Extremely low detection limits • Can detect a wide range of species

  14. Summary • Voltammetry is a very useful form of instrumental analysis • Wide range of applications • Assortment of electrodes allows for a very specific analysis of different chemicals • Capable of very low to moderate detection limits- parts per trillion to low ppm range

  15. References • “Chloride by Cathodic Stripping Voltammetry” Princeton Applied Research- Analytical Instrument Division • “Voltammetric Determination of Zinc, Cadmium, Lead, Copper, Thallium, Nickel, and Cobalt in Water Samples” Application note No. 231/2 E

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