Advanced Voltammetric Detection Methods for Metals Analysis

1. Tools II Voltammetric Detectors • Methods: Stripping, Metals • DPV • LC EC • Rat Brains

2. Anodic Stripping Voltammetry • General Process • Hanging Mercury Drop Electrode (HMDE) • Mercury Film Electrode • Non-mercury Electrode • Some electrode surface that forms an alloy with metals,OR, which catalyzes deposition • Preconcentrate metal by reducing from large volume into the alloy • Strip with an anodic sweep to oxidize from the alloy

3. Deposition current And time of deposition Concentration in the drop HMDE, spherically shaped ro Compare to the Randles-Sevich Equation:

4. For a Mercury Film Electrode the rate of arrival of the metal atoms at the surface For oxidation is altered due to the geometry of the electrode Compare to the peak for voltammetry at a thin layer electrode: Because the current at a thin film Electrode is of the same class as Current at a thin film, the peaks drop To baseline, resulting in better deiscrimination of Metals with similar potentials

5. Figure 11.8.6 bard and faulkner

6. Tool II Voltammetric Detectors • Methods: Stripping, DPV • Metals • LC EC • Rat Brains

12. Goal to use the electrstatic attraction for accumpulation Similar goal in using Nafion – also anionic material easily manipulated

13. 6] (a) Hickner, M. A.; Ghassemi, H.; Kim, Y. S.; Einsla, B. R.; McGrath, J. E. Chem. Rev. 2004, 104, 4587. (b) Haile, S. M. Acta Mater. 2003, 51, 5981. (c) Grot W. Chem. Ing. Tech. 1972, 44, 167.

14. Note the selectivity in potential and the discrimination between various metals Makes use of the enhanced microscopic surface area and electric fields of the Msall particles

15. JChem Ed 2007

16. Tool II Voltammetric Detectors • Methods: Stripping, DPV • Metals • LC EC, LC EC MS • Rat Brains

17. Many organics are easily oxidized Most solid metal electrodes do not oxidize in this range and so have low background current

19. Many others are easily reduced

29. All are candidates for voltammetric analysis

30. Signal to Noise in Voltammetric Analysis The limit of detection (LOD) is often defined as 3xpeak to peak signal due to noise • “Noise” in voltammetric methods is the result of • Competing or background electron transfer events originating in the • Solvent • Surface • 2. Currents arising from charging of the electrode surface The limit of detection is also affected by distortion of the signal due to IR error

31. Solutions to the IR and Capacitive Current Problems Signal Background These are on two different time scales! Modulate the time domain of the experiment to discriminate against capactive currents.

32. Square Wave Voltammetry 1 cycle E tp 1 2 Estep t 2Epulse

33. Kissinger Bard

34. AC Voltammetry Ac perturbation DC sweep

35. AC Voltammetry

36. Differential Pulse Voltammetry Want t

37. Summary AC voltammetry DP Voltammetry SW Voltammetry

43. GCE

44. LC EC

48. Control xD at a fixed distance: Rotating Disk electrode, RDE Wall Jet Electrode, WJE