1. ELECTROANALISIS (Elektrometri)
Potensiometri, Amperometri and Voltametri

2. Electroanalysis
Mengukur berbagai parameter listrik (potensial, arus listrik, muatan listrik, konduktivitas) dalam kaitannya dengan parameter kimia (reaksi ataupun konsentrasi dari bahan kimia)
Konduktimetri, Potensiometri (pH, ISE), Koulometri, Voltametri, Amperometri

3. Potensiometri
Pengukuran potensial listrik dari suatu Sel Elektrokimia untuk mendapatkan informasi mengenai bahan kimia yang ada pada sel tsb (conc., aktivitas, muatan listrik)
Mengukur perbedaan potensial listrik antara 2 electroda:
Elektroda Pembanding (E constant)
Elektroda Kerja/Indikator(sinyal analit)

4. Elektroda Pembanding
Ag/AgCl: Ag(s) | AgCl (s) | Cl-(aq) || .....

5. Elektroda Pembanding
SCE: Pt(s) | Hg(l) | Hg2Cl2 (l) | KCl(aq., sat.) ||.....

6. Elektroda Pembanding Reaksi/Potensial setengah selnya diketahui
Tidak bereaksi/dipengaruhi oleh analit yang diukur
Reversible dan mengikuti persamaan Nernst
Potensial Konstan
Dapat kembali ke potensial awal
stabil
Elektroda Calomel
Hg in contact with Hg(I) chloride (Hg/Hg2Cl2)
Ag/AgCl

7. Electroda Kerja Inert: Pt, Au, Carbon. Tidak ikut bereaksi.
Contoh: SCE || Fe3+, Fe2+(aq) | Pt(s)
Elektroda Logam yang mendeteksi ion logamnya sendiri (1st Electrode)
(Hg, Cu, Zn, Cd, Ag)
Contoh: SCE || Ag+(aq) | Ag(s)
Ag+ + e-  Ag(s) E0+= 0.799V
Hg2Cl2 + 2e  2Hg(l) + 2Cl- E-= 0.241V
E = log [Ag+] V

8. Electroda Kerja 1st kind Ecell=Eindicator-Ereference Metallic
1st kind, 2nd kind, 3rd kind, redox
1st kind
respond directly to changing activity of electrode ion
Direct equilibrium with solution

9. 2nd kind 3rd kind Precipitate or stable complex of ion Ag for halides
Ag wire in AgCl saturated surface
Complexes with organic ligands
EDTA
3rd kind
Electrode responds to different cation
Competition with ligand complex

10. Metallic Redox Indictors
Inert metals
Pt, Au, Pd
Electron source or sink
Redox of metal ion evaluated
May not be reversible

11. Membrane Indicator electrodes
Non-crystalline membranes:
Glass - silicate glasses for H+, Na+
Liquid - liquid ion exchanger for Ca2+
Immobilized liquid - liquid/PVC matrix for Ca2+ and NO3-
Crystalline membranes:
Single crystal - LaF3 for FPolycrystalline
or mixed crystal - AgS for S2- and Ag+
Properties
Low solubility - solids, semi-solids and polymers
Some electrical conductivity - often by doping
Selectivity - part of membrane binds/reacts with analyte

12. Glass Membrane Electrode

13. Ion selective electrodes (ISEs)
A difference in the activity of an ion on either side of a selective membrane results in a thermodynamic potensial difference being created across that membrane

14. ISEs

15. Combination glass pH Electrode

16. Proper pH Calibration E = constant – constant.0.0591 pH
Meter measures E vs pH – must calibrate both slope & intercept on meter with buffers
Meter has two controls – calibrate & slope
1st use pH 7.00 buffer to adjust calibrate knob
2nd step is to use any other pH buffer
Adjust slope/temp control to correct pH value
This will pivot the calibration line around the isopotensial which is set to 7.00 in all meters
Slope/temp control pivots
line around isopotensial
without changing it mV mV
Calibrate knob raises
and lowers the line
without changing slope pH pH

17. Liquid Membrane Electrodes
Persamaan nikolsky untuk pengukuran sampel campuran dengan kurva kalibrasi dan standard adisi

18. Solid State Membrane Electrodes
Ag wire
Solid State Membrane Chemistry
Membrane
Ion Determined
LaF3
F-, La3+
AgCl
Ag+, Cl-
AgBr
Ag+, Br-
AgI
Ag+, I-
Ag2S
Ag+, S2-
Ag2S + CuS
Cu2+
Ag2S + CdS
Cd2+
Ag2S + PbS
Pb2+
Filling
solution
with fixed
[Cl-] and
cation that
electrode
responds to
Ag/AgCl
Solid state membrane
(must be ionic conductor)

19. Solid state electrodes

20. VOLTAMETRI Pengukuran arus sebagai fungsi perubahan potensial
POLAROGRAFI:
Heyrovsky (1922): melakukan percobaan voltametri yang pertama dengan elektroda merkuri tetes (DME)
Cu2+ + 2e → Cu(Hg)

22. Mengapa elektron berpindah
Reduction
Oxidation EF
Eredox
Eredox E E EF

23. Steps in an electron transfer event
O must be successfully transported from bulk solution (mass transport)
O must adsorb transiently onto electrode surface (non-faradaic)
CT must occur between electrode and O (faradaic)
R must desorb from electrode surface (non-faradaic)
R must be transported away from electrode surface back into bulk solution (mass transport)

24. Mass Transport or Mass Transfer
Migration – movement of a muatan listrik listrik particle in a potensial field
Diffusion – movement due to a concentration gradient. If electrochemical reaction depletes (or produces) some species at the electrode surface, then a concentration gradient develops and the electroactive species will tend to diffuse from the bulk solution to the electrode (or from the electrode out into the bulk solution)
Convection – mass transfer due to stirring. Achieved by some form of mechanical movement of the solution or the electrode i.e., stir solution, rotate or vibrate electrode
Difficult to get perfect reproducibility with stirring, better to move the electrode
Convection is considerably more efficient than diffusion or migration = higher arus listriks for a given concentration = greater analytical sensitivity

25. Nernst-Planck Equation
Diffusion
Migration
Convection
Ji(x) = flux of species i at distance x from electrode (mole/cm2 s)
Di = diffusion coefficient (cm2/s)
Ci(x)/x = concentration gradient at distance x from electrode
(x)/x = potensial gradient at distance x from electrode
(x) = velocity at which species i moves (cm/s)

26. Diffusion I = nFAJ Fick’s 1st Law
Solving Fick’s Laws for particular applications like electrochemistry involves establishing Initial Conditions and Boundary Conditions

27. Simplest Experiment Chronoamperometri

28. Simulation

29. Recall-Double layer

30. Double-Layer charging
Charging/discharging a capacitor upon application of a potensial step
Itotal = Ic + IF

31. Working electrode choice
Depends upon potensial window desired
Overpotensial
Stability of material
Conductivity
contamination

32. electron transfer to the electroactive species.
The polarogram
points a to b
I = E/R
points b to c
electron transfer to the electroactive species.
I(reduction) depends on the no. of molecules reduced/s: this rises as a function of E
points c to d
when E is sufficiently negative, every molecule that reaches the electrode surface is reduced.

33. Dropping Mercury Electrode
Renewable surface
potensial window expanded for reduction (high overpotensial for proton reduction at mercury)

34. Polarography A = 4(3mt/4d)2/3 = 0.85(mt)2/3
Density of drop
Mass flow rate of drop
We can substitute this into Cottrell Equation
i(t) = nFACD1/2/ 1/2t1/2
We also replace D by 7/3D to account for the compression of the diffusion layer by the expanding drop
Giving the Ilkovich Equation:
id = 708nD1/2m2/3t1/6C
I has units of Amps when D is in cm2s-1,m is in g/s and t is in seconds. C is in mol/cm3
This expression gives the arus listrik at the end of the drop life. The average arus listrik is obtained by integrating the arus listrik over this time period
iav = 607nD1/2m2/3t1/6C

35. Polarograms E1/2 = E0 + RT/nF log (DR/Do)1/2 (reversible couple)
Usually D’s are similar so half wave potensial is similar to formal potensial. Also potensial is independent of concentration and can therefore be used as a diagnostic of identity of analytes.

38. Other types of Polarography
Examples refer to polarography but are applicable to other votammetric methods as well
all attempt to improve signal to noise
usually by removing capacitive arus listriks

39. Normal Pulse Polarography

40. NPP advantage

41. Differential pulse voltametri

42. DPP vs DCP Ep ~ E1/2 (Ep= E1/2±DE/2) s = exp[(nF/RT)(DE/2)]
where DE=pulse amplitude
s = exp[(nF/RT)(DE/2)]
Resolution depends on DE
W1/2 = 3.52RT/nF when DE0
Improved response
because charging arus listrik
is subtracted and adsorptive
effects are discriminated against.
l.o.d M

43. Resolution

44. Stripping voltametri Preconcentration technique.
1. Preconcentration or accumulation step. Here the analyte species is collected onto/into the working electrode
2. Measurement step : here a potensial waveform is applied to the electrode to remove (strip) the accumulated analyte.

45. Deposition potensial

46. ASV

47. ASV or CSV

50. Multi-Element

51. Standard Addition

52. Cyclic voltametri
Cyclic voltametri is carried out at a stationary electrode.
This normally involves the use of an inert disc electrode made from platinum, gold or glassy carbon. Nickel has also been used.
The potensial is continuously changed as a linear function of time. The rate of change of potensial with time is referred to as the scan rate (v). Compared to a RDE the scan rates in cyclic voltametri are usually much higher, typically 50 mV s-1

53. Cyclic voltametri
Cyclic voltametri, in which the direction of the potensial is reversed at the end of the first scan. Thus, the waveform is usually of the form of an isosceles triangle.
The advantage using a stationary electrode is that the product of the electron transfer reaction that occurred in the forward scan can be probed again in the reverse scan.
CV is a powerful tool for the determination of formal redox potensials, detection of chemical reactions that precede or follow the electrochemical reaction and evaluation of electron transfer kinetics.

54. Cyclic voltametri

55. Cyclic voltametri
For a reversible process
Epc – Epa = 0.059V/n

56. The Randles-Sevcik equation Reversible systems

57. The Randles-Sevcik equation Reversible systems
n = the number of electrons in the redox reaction
v = the scan rate in V s-1
F = the Faraday’s constant 96,485 coulombs mole-1
A = the electrode area cm2
R = the gas constant J mole-1 K-1
T = the temperature K
D = the analyte diffusion coefficient cm2 s-1

58. The Randles-Sevcik equation Reversible systems
As expected a plot of peak height vs the square root of the scan rate produces a linear plot, in which the diffusion coefficient can be obtained from the slope of the plot.

59. Cyclic voltametri

60. Cyclic voltametri

61. Cyclic voltametri

62. Cyclic voltametri – Stationary Electrode
Peak positions are related to formal potensial of redox process
E0 = (Epa + Epc ) /2
Separation of peaks for a reversible couple is 0.059/n volts
A one electron fast electron transfer reaction thus gives 59mV separation
Peak potensials are then independent of scan rate
Half-peak potensial Ep/2 = E1/2  0.028/n
Sign is + for a reduction