6'1 Introduction

1
6.1 Introduction
polarogaphy
liquid electrodes
woking electrodes
solid electrodes
voltammetry
2
6.2 Foundamentals of general polarography
6.2.1 The introduction of the classical
polarography
Design Fig6.2-1
e.g. Polarograms ( i vs E relationships ) of
Cd2 Fig6.2-2
3
The half-wave potential is indepent of the
concentration
The specification of polarograms determination
4
6.2.2 the form of polarogram
The polarogram has three current regions
The residual current (ir) region

Diffusion current (id) region
Limiting current (il) region
5
6.2.3 The specification of electrode
Polarization electrode
Unpolarization electrode
The advantages of the dropping mercury
electrode (DME)
6
6.3 Diffusion current equation
6.3.1 Ilkovic diffusion current equation
id k n D1/2 m2/3 t1/2 Cox
7
6.3.2 The factors determining the diffusion
current
The analyte concentration
The characteristics of the capillary
The effect of dropping mercury potential
Temperature effect
8
6.4 Factors affecting the shape of the polargram
The residual current Fig6.4-1 Fig6.4-2
The current maxima Fig6.4-3
The presence of oxygen Fig6.4-4
9
6.5 The quantitative analytical method of
polarography
6.5.1 The determination of diffusion current
Parallel method Fig6.5-1
Thritangential method Fig6.5-2
10
6.5.2 The quantitative method of polargraphy
Directive comparative method
Working curve Fig6.5-3
Standard addition method Fig6.5-4
11
6.6 Introduction about new polarography
6.6.1 Polaro-catalysing wave
6.6.2 Stripping analysis method
6.6.3 Linear sweep(dc) oscillo- polarography
Basic line Fig6.6-1 Fig6.6-2
12
6.6.4 Circular voltammetry
Fundamental Fig6.6-3
Application Fig6.6-4
13
It is special electrolytic design which
consists of
a. Electrolytic cell
b. Voltmeter V
c. Ampere meter
14
Its specialties show
a. Large areas of reference electrode
b. Small areas of working electrode
c. The infinite dilution
15
As the half-wave potential is independent of
solution analyte concentration and dependant
primary on the nature of analyte.
16
It can be used for the identification of analyte
species taking part in the electrode reaction.
17
In general, they are ascribed to the
convection of the solution layer in the vicinity
of the working electrode which is induced by the
inhomogeneous charge distribution in the dropping
Hg electrode.
18
Elimination
The current maxima can be supppressed by the
addition of polarographically inactive
surfactants, such as gelation, methyl red or
other dyes to obtain the desired effect.
19
Elimination methods
? In neutral or alkaline media by Na2SO3 solution
? In solution of all pH by N2 or Ar or H2 etc.
? In acid solution by ascorbic acid
20
Then
21
The principles of qualitative quantitative and
analysis Fig.6.6
? The basis for quantitative analysis
ip Kn3/2D1/2V1/2AC
22
? The basis for qualitative analysis
Peak potential is only decided by the
properties of reducing material under certain
condition (temperature, the fixed bottom solution
).
23
Working electrode, static electrode such as
? Suspending electrode
? Stationary electrode
24
Which was mainly used to study the mechanism
of electrode process, such as

25
The determination of its reverse
26
The distance between two peaks is farther,
the more irreverent it is.