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electrode surface

stirred δ : const. ( əC A / əx) = conc. gradient = slope of conc. profile α diffusion rate. i = nFAD A ( ə C A / ə x) = nFAD A [(C A - C A º ) / δ ]. as C A º → 0 i l = nFAD A C A / δ = k A C A. unstirred δ: ↑ w time. For A + ne - = P

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electrode surface

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  1. stirred δ: const (əCA / əx) = conc. gradient = slope of conc. profile αdiffusion rate i = nFADA (əCA/ əx) = nFADA [(CA - CAº) /δ] as CAº → 0 il = nFADACA / δ = kACA unstirred δ: ↑w time For A + ne- = P Eapp = E1/2 – (0.0592 / n) log (CPº/ CAº) CPº : surface conc. of product P CAº : surface conc. of analyte A unstirred δ: ↑w time electrode surface

  2. Solution: stirred vs. unstirred Eappl: linear scan vs. stepped 1 ms Eappl 5 ms 10 ms diffusion layer ↑ w time i α(əCA/ əx) conc. gradient α diffusion rate

  3. FIGURE 25-9Current response to a stepped potential for a planar electrode in an unstirred solution. (a) Excitation potential. (b) Current response.

  4. FIGURE 25-10Concentration distance profiles during the diffusion-controlled reduction of A to give P at a planar electrode. (a) Eappl = 0 V. (b) Eappl = point Z in Figure 25-6; elapsed time: 1, 5, and 10 ms.

  5. DME 0.1 M KCl FIGURE 25-16 Vol’tammogram for the reduction of oxygen in an air-saturated 0.1-M KCl solution. The lower curve is for a 0.1-M KCl solution in which the oxygen is removed by bubbling nitrogen through the solution. air-saturated deaerated (by N2)

  6. Amperometric Detector in Liquid Chromatography Amperometry: to measure i at the fixed applied potential FIGURE 25-17(a) A schematic of a voltammtric system for detecting electroactive species as they elute from a column. The cell volume is determined by the thickness of the gasket. i Eapplied E amperometric 墊片 thin-layer cell

  7. FIGURE 25-17(b) Detail of a commercial flow cell assembly.

  8. FIGURE 25-17(c) Configurations of working electrode blocks. Arrows shown the direction of flow in the cell.

  9. Peter T. Kissinger Professor— Analytical Chemistry Department of Chemistry, Purdue University Professor Kissinger is a part time faculty member and entrepreneur who founded the drug development company Bioanalytical Systems, Inc. He regularly counsels students on career opportunities in the pharmaceutical industry and is active in the Indiana Instrumentation Institute (III) and development of the Purdue Research Park. B.S., 1966, Union College; Ph.D., 1970, University of North Carolina; Postdoctoral Associate, 1970-1972.

  10. Parkinson’s Disease 巴(帕)金森症 • 原因不明的退化性腦疾病 • 缺少Dopamine(多巴胺) – a neurotransmitter (腦神經傳導物質) • 症狀： 顫抖, 肌肉僵硬, 動作緩慢 • 研究方法：mouse(小白鼠)，rat (大白鼠) LC – UV LC – Fluorescence LC – EC

  11. LC-EC pump micro-dialysis 微透析

  12. UV/Vis LC Detector From column To waste

  13. Clark oxygen sensor 1956 FIGURE 25-18 The Clark voltammetric oxygen sensor. Cathodic reaction: O2 + 4H+ + 4e- → 2H2O. Anodic reaction: Ag + Cl- → AgCl(s) + e- To determine the dissolved oxygen in a variety of aqueous environment, e.g., sea water, blood, sewage, etc. Pt Teflon or Polyethylene (PE) Ag

  14. Clinical test 尿素氮 (腎功能) BUN (Blood Urine Nitrogen) FIGURE 23-13Enzyme electrodes for measuring urea. urease (NH2)2CO + 2H2O + H+2NH4+ + HCO3- (23-23) urea pH 7.5 2NH3 + 2H+

  15. Ch1 Introduction P.10 Immunosensors 免疫感測器 ISE Antigen = target analyte

  16. Au FIGURE 21-14Surface plasmon resonance. Laser radiation is coupled into the glass substrate coated with a thin metal film by a half-cylindrical prism. If total internal reflection occurs, an evanescent wave is generated in the medium of lower refractive index. This wave can excite surface plasmon waves. When the angle is suitable for surface plasmon resonance, a sharp decrease in the reflected intensity is observed at the detector.

  17. Ch25 Voltammetry P.734 antibody antigen = target analyte Au film Surface plasmon resonanace: a label-free immunosensor

  18. antigen antibody = target analyte Label 標示基 Fluorescent molecule W.E. FIGURE 25-19(a)A: electrode containing immobilized antibody (Y); B: binding of target analyte (▼) to electrode-bound antibody; C: binding of alkaline phosphatase-labeled antibody to electrode-bound analyte; D: application of 320 mV to the electrode and addition of hydroquinone diphosphate (HQDP). Electrochemical oxidation of AP-generated hydroquinone (HQ) generates a current at the electrode that is proportional to the amount of analyte bound to the electrode. hydroquinone diphosphate enzyme (alkaline phosphatase) Sandwich assay i α [analyte] hydroquinone quinone

  19. FIGURE 25-19(b) Photograph of the biosensor showing the arrangement of lrOx 1-mm-diameter working electrodes, 4-mm-diameter counter electrode, 7-mm-outside-diameter Ag-AgCl reference electrode, and electrical contacts on the substrate (28 × 35 × 1 mm). For clarity, the sample well is not shown.

  20. titration reaction: Stirred P: electro-inactive i Analyte Reagent A + R → P Eapplied E A + R A R end point at a fixed applied potential X 20

  21. rotate the electrode FIGURE 25-21(a) Side view of an RDE showing solution flow pattern. (b) Bottom view of a disk electrode. rotating disk electrode, RDE

  22. FIGURE 25-21 (c) Photo of a commercial RDE. (d) Bottom view of a ring-disk electrode. X

  23. Rotating Disk Electrode, RDE ● The most common method for obtaining a rigorous description of the hydrodynamic flow of stirred solution is based on a rotating disk electrode. ●Numerous studies of the kinetics and the mechanisms of electrochemical reaction have been performed with rotating disk electrode. Levich equation: 修訂錯誤 il = 0.620 n F AD2/3CAν-1/6ω1/2(25-15) limiting i ν : kinematic viscosity (cm2/s) ω : angular velocity = 2 π f f :rotation speed ( r p m )

  24. hydrodynamic FIGURE 25-22Disk (a) and ring (b) current for reduction of oxygen at the rotating-ring-disk electrode. X

  25. DME 0.1 M KCl FIGURE 25-16 Vol’tammogram for the reduction of oxygen in an air-saturated 0.1-M KCl solution. The lower curve is for a 0.1-M KCl solution in which the oxygen is removed by bubbling nitrogen through the solution. air-saturated deaerated (by N2)

  26. Cyclic Voltammetry (CV) 循環伏安法 switching potential reverse scan forward scan in unstirred soln scan rate: 50 mV/s Ei (initial potential) 23 װ potential waveform

  27. for reversible reaction : Epa – Epc = 0.0592 / n ipc≈ ipa Eº’ = (Epc + Epa) / 2 for diffusion-controlled reax : ipαν1/2 FIGURE 25-24 (a) Potential versus time waveform (b) cyclic voltammogram for a solution that is 6.0 mM in K3Fe(CN)6 and 1.0 M in KNO3. Fe(CN)63- + e-→ Fe(CN)64- a: anodic 氧化的 c: cathodic還原的 no reax at Ei Stationary soln Pt-disk electrode Fe(CN)64- → Fe(CN)63- +e-

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