??? ?????(Voltammetry)

1

• ??? ?????(Voltammetry)
• 5-1 ??????????
• ????????????
• ????????????????????????,???????????-??????
  ?????????????????????????

??????????????????? ????????????,??????
??????????????????????,??????
2

• 1922 ? ????? ????? J.Heyrovsky
• ?????,1959??Nobel?
• 1934 ? ???? Ilkovic, ???????
• ?,??????????????
• 20??40???? ?????????????????????(1944?)??????(
  1952?)??????(1958?)??????(1970?)
• 20??40???? ????????????????????????????????????
  ??????????????????????????????,???????????????????
  ????????

3
??????????
??????????????????,?????????????????
??????
??????
U? ? i
U?- Ud iR
U????????R???? ??? Ud??????
4

5

• ???????????

?????? ??????
1. ?? 2. ??? 3. ??
????????????????????????,?????????????????????
6

• ???? ????????????????????????????????????????

????? ?????????????????????????????????????
??????????????????????????,??????????????????????
???????????????,?????????????,????????????,???????
???????????????????
7

• ????????????

8

9
(No Transcript)
10
(No Transcript)
11

12

13
(No Transcript)
14

15

• ??????I V?????,????i Ede?????,??????????,?????
  ????

V ( ESCE -Ede ) i R
? R are very little in polarographic
electrolysis
V ESCE - Ede -Ede( vs. SCE)
??????Id?????????????
????E1/2?????????????
16

• 5-2 ?????????????
• ????????????

17

• ??????????????????

M n ne- Hg M(Hg)
?????????????????????
i K (C e??-C e??)
???????????
Id K C ??
18
??????? ???????
19

• ??????Ilkovic equation---
• diffusion current equation

?????
K 607 n D1/2 m2/3 t1/6 id 607n D1/2 m2/3
t1/6 C
?????????(mmol.L-1)
????????????(mA)
???????????(cm2.sec-1)
???? (sec)
????(mg.sec-1)
20

• ???????????????

1. 1??????????
2. ????????????????
3. ?????????

2???????m?????t??? ??????????????????
3???????????????? ??????????????????
21

• ??????????????

1.?????
hs KCs hx KCx
????????,??
?????????????????? ???????
22

• 2 ?????(?????)
• ??????????,??????,?????????h,?h C
  ?,???????,?hx??Cx ?
• ???????????,????????????
• 3 ?????

???????????,?????????
????K,??
23

24

• 5-3 ????????????
• ??????????????

???????????,????? ??????
????? -id kACA ???? -i
kA(CA- CAe)
25

• ??

??????????????????????????????,???????????????????
??,????
CBe ? - i
26

• ?

? i ½ id ?, ?????????1,?????????????????E,?????
??????????,????????,???????????,????????????(
halfwave potential E1/2)
?????????????,?????????????,?????????????????????
??
27
?????
?? 1????????,?????? E1/2??????
2??????????????????????,????????
28
(No Transcript)
29
(No Transcript)
30

31

• ?????????????????
• ??????????????????????????????????????????
  ?????????????????

1. ???? (residual current)???
?????????
???????????????? ????,??????????????? ??,????????
? ???????????????? ?,????????????
??????????????
32
Null potential point
33
(No Transcript)
34
?????????????????????,?????????,?????????????????
????????????????????????????(?lt10-5M)???,?????????
???????????,??????????,?????????(??10-7A???)??(Why
some 10-7A? Please refer to page 157158, in the
teaching book), ??????????????????????????????????
??????
35

• 2? ????(migration current)

?????????,????????????????????????????,????
?? ?????????????
3? ???? (polarographic maximum)
???????????,???????????????????????,?????
????????,?????????????????????????????????,??????
?????????
36

• ?????(??)?????????
• (???)???,?????????
• ?????????????????,
• ????????????(?????)
• ????
• ?????(???)??????????
• ?????
• ??????????,
• ???????????????????

37
?Maximum (or malformed peak ) ??(???)
??????,???? ??????,???????, ??????????????
???????,?????? ?????????????? ?),???????? ????
??????, eg. ???,????,??????, Triton X-100?, 0.01
38

• 4? ??

??????????????,?????,????????
E1/2-0.05V(vs.SCE) E1/2 -0.94V(vs.SCE)

• ??????????????????
• ? ??????????????
• ???,????
• ? ????????Na2SO3,???
• ??????????????
• ? ?????????Na2CO3 ?
• Fe??????

39

• 5? ??
• ???????(?????????0?),???????????????????????
  ????????????,?????????-1.2-1.4V?????????????,????
  ?????????????????-2.1V,???????????????????????????
  ????pH??????????

40

• 5-5 ???????

???(advantages)
???? 10-2 10-4mol.L-1 ????? 2
????????4 5????? ??????? ????????,????
??????
???(Disadvantages)
????????????? ??????????? ???????, ?E1/2
100mV
41

42

• 5-7 ????????
• ??????????????

43
?????(Classical polarography) ???????????
0.2V/min, ????? ???100 ?? ????????
?????? (Single-wseep
polarography) ??????????? 0.25V/sec, ???
??????? ???????? ?????(Oscillographic
polarograph)
44
ip and Ep are respectively peak current and peak
voltage U is toothed wave voltage
(?????)
45

• ???????????????

???????,??????????????????????
ip 2.69105n3/2 D1/2 u 1/2 AC ??????,A?????
??? Ep ?????E1/2????
46

47

• ????????????????

???? 10-7mol.L-1, ?????? ?2-3
???? ???????? ??????? ???????? 35 50mV
??? ????????? ?????????????, (????)?????
48

49

• ??????????

? Cyclic voltammetry ???????????
???????????????? ????????????
50

• ????????????????????????????,?????????????????????
  ?????,???????????????????

???????,DEp gt 56.5/n(mV), ipa / ipc lt 1?
?Ep??,?????????,???????????
51

?????????????
52

????????????????????
53

• 5-8 ???????
• ?????????????

54

• ????????????????

??????????????? 5???????????????????,??????????
55

• ????????????
• 1????????????????????????????????????????????
  ???????????????
• 2?????????????????????????????????????????????
  ?
• 3???????????????(RC),?????????????????????

56

• 4???????????????????????,?????????????????????
  ?,??????
• 5?????????????????,?????????????????????
• 6?????????????,?????????????????????

57
5-9 Pulse polarography
58
(No Transcript)
59
(No Transcript)
60
(No Transcript)
61
(No Transcript)
62
???????????????????
63
5-10 Stripping voltammetry
???????????????,????????????,????????
??????,?????????,???????????????,?????????????????
??????
64
(No Transcript)
65
(No Transcript)
66
(No Transcript)
67
(No Transcript)
68
Electrodes in stripping voltammetry
? Hung mercury electrode ? glass carbon
electrode mercury plating
(???????????)
Problems
Compared with other polarographic methods, how
about the sensitivity of square wave
polarography? what advantages do mercury hung
electrode and mercury membrane electrode
have ?
69
(No Transcript)
70
(No Transcript)
71
(No Transcript)
72
(No Transcript)
73
(No Transcript)
74
5-11 ?????????(Amperometric titration with
single indicating electrode, polarographic
titration)
Amperometric titration keeping potential
constant Potentiometric titration keeping
current constant or at null-current
75
a analyte is electroactive (able to be reduced
on electrode), but the titrant is not b
analyte and titrant are all able to be reduced on
the polar electrode
76
Electrodes
Reference electrode calomel electrode,
mercury pool
electrode Working electrode dropping mercury
electrode,
solid microelectrode
Advantages
Solid microelectrode can be used wide
linear range. 0.1 10-4mol.L-1 Using a
electrode with a big area, DL can be down to
10-6 mol.L-1 Back titration can increase
upper limit of determination some
electro-inactive materials can also be measured
using electro-active titrant.
77
Example
78
5-12 ?????????(????) (Dead-stop end point
titration)
79

• 5- 13 ?????????
• (potentiometric titration with double
• indicating electrodes)

? ? ? ? ? ? ? ?
80