electrode surface

stirredδ: const

unstirredδ: ↑w time

unstirredδ: ↑w time

i = nFADA (əCA / əx)

= nFADA [(CA - CAº ) /δ]

(əCA / əx) = conc. gradient

= slope of conc. profile

α diffusion rate as CAº → 0

il = nFADACA / δ = kACA

For A + ne- = P

Eapp = E1/2 – (0.0592 / n) log (CPº / CAº) CPº : surface conc. of product PCAº : surface conc. of analyte A

1 ms

5 ms

i α(əCA / əx) conc. gradient

α diffusion rate

10 ms

Eappl

Solution: stirred vs. unstirredEappl: linear scan vs. stepped

diffusion layer ↑ w time

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

FIGURE 25-10 Concentration 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.

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.

deaerated (by N2)

air-saturated

DME

0.1 M KCl

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.

墊片

Amperometric Detector in Liquid Chromatography

Amperometry: to measure i at the fixed applied potential

i

Eapplied

E

thin-layer cell

amperometric

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

FIGURE 25-17(c) Configurations of working electrode

blocks. Arrows shown the direction of flow in the cell.

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.

Professor— Analytical Chemistry Department of Chemistry, Purdue University

Peter T. Kissinger

B.S., 1966, Union College; Ph.D., 1970, University of North Carolina; Postdoctoral Associate, 1970-1972.

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

pump

LC-EC

micro-dialysis

微透析

From column

To waste

UV/Vis LC Detector

FIGURE 25-18 The Clark voltammetric oxygen sensor. Cathodic reaction: O2 + 4H+ + 4e- → 2H2O.

Anodic reaction: Ag + Cl- → AgCl(s) + e-

1956

Clark oxygen sensor

To determine the dissolved oxygen in a variety of aqueous environment, e.g., sea water, blood, sewage, etc.

Pt

Ag

Teflon orPolyethylene (PE)

(NH2)2CO + 2H2O + H+ 2NH4+ + HCO3

- (23-23)urease

pH 7.5urea

2NH3 + 2H+

Clinical test

尿素氮 ( 腎功能 ) BUN (Blood Urine Nitrogen)

FIGURE 23-13 Enzyme electrodes for measuring urea.

P.10Ch1 Introduction

ISE

Immunosensors 免疫感測器

Antigen = target analyte

FIGURE 21-14 Surface 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.

Au

P.734Ch25 Voltammetry

antibody

Au film

antigen= target analyte

Surface plasmon resonanace: a label-free immunosensor

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.

Label 標示基Fluorescent molecule

enzyme

(alkaline phosphatase)

Sandwich assay

antibody antigen= target analyte

W.E.

hydroquinone diphosphate

hydroquinone

quinone

i α [analyte]

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.

at a fixed applied potential

end point

A R A + R

A + R → P

Analyte Reagent i

E

Eapplied

titration reaction:Stirred

P: electro-inactive

X20

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

rotate the electrode

rotating disk electrode, RDE

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

electrode.

X

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.

il = 0.620 n F A D2/3 CA ν-1/6 ω 1/2 (25-15)

ν : kinematic viscosity (cm2/s)

ω : angular velocity

= 2 π f

f : rotation speed ( r p m )

limiting i

修訂錯誤Levich equation:

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

hydrodynamic

X

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.

deaerated (by N2)

air-saturated

DME

0.1 M KCl

Cyclic Voltammetry (CV)

potential waveform

Ei (initial potential)

forward scanreverse scan

switching potential

in unstirred soln

scan rate: 50 mV/s

װ

循環伏安法

23

FIGURE 25-24 (a) Potential versus time waveform (b) cyclic voltammogram for a solution th

at is 6.0 mM in K3Fe(CN)6 and 1.0 M in KNO3.

Stationary soln

Pt-disk electrode

no reaxat Ei

Fe(CN)63- + e- → Fe(CN)6

4-

Fe(CN)64- → Fe(CN)6

3- + e-

for reversible reaction :

Epa – Epc = 0.0592 / n

ipc ≈ ipa

Eº’ = (Epc + Epa) / 2

for diffusion-controlled reax :

ip α ν1/2

a: anodic 氧化的c: cathodic　還原的