《电分析化学》（英文版）Lecture6 An introduction to electrochemical Methods(contd)

Electroanalytical Chemistr Lecture #t6 An introduction to electrochemical Methods(cont'd

Electroanalytical Chemistry Lecture #6 An Introduction to Electrochemical Methods (cont’d)

Q: What Experiment is This? Excitation Name of experiment E type of excitation time Response R response slope time Deficiency

Q: What Experiment is This? Name of experiment type of excitation Response – i  ____ – slope Deficiency Excitation Response time time E I to to t

What Experiment Is This? Name of experiment Excitation E Type of excitation time Response Response Q intercept slope time

What Experiment Is This? Name of experiment Type of excitation Response – Q  ____ – intercept – slope Excitation Response time time E Q to to t Qdl

Excitation Q: What Is This E° Experiment? E Name of experiment Time. s E Excitation Response E of v abD]

Q: What Is This Experiment? Name of experiment Excitation Response – i  ____ – Ep ____ of  – E’ = _____________ Time, s Eapp, V Excitation E1 E2 Eapp, V I, A Ep E1 E2 Response E o E o X X

Excitation Cyclic Voltammetry(Cv) E Important Time. s parameters Ea and e pc and ac E △E=Ea-Ep E R-ne=o abD]

Cyclic Voltammetry (CV) Important parameters: – Epa and Epc – ipc and iac – E’ – DE = |Epa - Epc| Time, s Eapp, V Excitation E1 E2 Eapp, V I, A Epa Epc E1 E2 Response R - ne- = O

For Nernstian Cv AEp=Epa-Epc=59/n mV at 25C independent of v E0=(E。+E/2 pa pc pc pa

For Nernstian CV DEp = |Epa - Epc| = 59/n mV at 250C – independent of  Eo = (Epa + Epc)/2 Ipc/Ipa = 1

For nernstian process Potential excitation controls [rlio] as in Nernst equation app =E0-0.059/nog [R][O] if En>eo ol ri and ox occurs app if eapp eo, [] [r] and red occurs i.e., potential excitation CONTROLS [RJIOI

For Nernstian Process Potential excitation controls [R]/[O] as in Nernst equation: Eapp = E0 - 0.059/n log [R]/[O] if Eapp > E0 , [O] ___ [R] and ox occurs if Eapp < E0 , [O] ___ [R] and red occurs i.e., potential excitation CONTROLS [R]/[O]

Criteria for nernstian process En independent of scan rate ip oc v2( diffusion controlled) pdpa 1 chemically reversible)

Criteria for Nernstian Process Ep independent of scan rate ip   1/2 (diffusion controlled) Ipc/Ipa = 1 (chemically reversible)

Quasi-reversible or Irreversible Quasi-reversible △E>59 mV and△ En increases with Increasing v iR can mascarade as QR system Irreversible: chemically -no return wave sloW ET-2 waves do not overlap

Quasi-reversible or Irreversible Quasi-reversible: – DEp > 59 mV and DEp increases with increasing  – iR can mascarade as QR system Irreversible: – chemically - no return wave – slow ET - 2 waves do not overlap

EXAMPLE Electrocatalytic Oxidation of guanine in dna 400120010008006004002000200 Top: non-faradaic contribution Bottom: shape and 1400120010008006004002000-200 magnitude of redoX Figure 1. (A Cyclic voltammograms taken at 10 Vis for bare To in 50 mM sodium phosphate, pH 7(dashed line) and for a DNA- waves modified electrode in 10 uM Ru(bpy)t(solid line).(B)Cyclic voltammograms obtained after subtraction for 10 uM Ru(bpy t at an unmodified electrode (dashed line) and at the DNA-modified electrode from (A)(solid line). Subtractions used as a background scan of bare ITo in 50 mM sodium phosphate, as shown as the dashed line in(A) P. M.Armistead; HHThorp Anal. Chem. 2000, 72, 3764-70

EXAMPLE: Electrocatalytic Oxidation of Guanine in DNA Top: non-faradaic contribution Bottom: shape and magnitude of redox waves P.M.Armistead; H.H.Thorp Anal. Chem. 2000, 72, 3764-70