Polarography is an electrochemical technique for analyzing electro reducible or oxidizable elements by measuring current between two electrodes with applied voltage. The document outlines various types of polarography, including direct current, normal pulse, differential pulse, alternating current, and square wave polarography, each with distinct methodologies and advantages. It highlights the detection limits and benefits of each type, emphasizing improved sensitivity and reduced contamination potential in measurements.

1. TYPES OF
POLAROGRAPHY

2. INTRODUCTION
• Polarography is a technique used for the
qualitative and quantitative analysis of
electro reducible or oxidizable elements
or groups.
• It is a electrochemical technique of
analyzing solution that measure the
current flowing between two electrodes
in the solution as well as the gradually
increasing applied voltage to determine
respectively the concentration of solute
and its nature.

3. PRINCIPLE OF POLARIOGRAPHY
The principle in polarography is that a gradually increasing negative potential (voltage) is applied
between a polarisable and non-polarisable electrode and the corresponding current is recorded.
• Polarisable electrode: Dropping Mercury electrode
• Non-polarisable electrode: Saturated Calomel electrode
• From the current-voltage curve (Sigmoid shape), qualitative and quantitative analysis can be
performed.
• This technique is called as polarography.
• The instrument used is called as polarograph.
• The current-voltage curve recorded is called as polarogram.

4. TYPES OF POLAROGRAPHY
• Direct current polarography (DCP)
• Normal pulse polarography (NPP)
• Differential pulse polarography (DPP)
• Alternating current polarography (ACP)
• Square wave polarography (SWP)

5. 1. DIRECT CURRENT POLAROGRAPHY
(DCP)
• In DC polarography, a continuously increasing
DC potential is applied to dropping mercury
electrode DME and corresponding current is
recorded in a continuous manner.
• It consist of droping mecury electrode with a
diametre of capilary of range 20-50 micro
metre and droplet time is 2 to 12 seconds so
5-30 drops can be produced per minute.
• The applied potential range from +0.4 to -1.8V.
• Detection limit is up to 10^-3 to 10^-4 M.

6. ADVANTAGES OF DCP
• This technique was useful to determine the
concentration of almost all organic and inorganic
analyte.
• Its surface is reproducible, smooth and
continously renewed. it eliminate or minimizes
the contamination possibility
• It is sensitive as compared to earlier classical
technique.

7. 2. NORMAL PULSE POLAROGRAPHY
• It is also called as large amplitude pulse
polarography.
• In this technique a constant base line potential
is applied to DME and pulse of increasing
amplitude are super imposed on it.
• The pulse is applied only for 50mS at the end of
drop time while current Is recorded just for lost
17mS at the end of pulse.
• After each pulse the capillary is mechanically
tapped and mercury drop falls down.
• The resultant polarogram is sigmoidal in nature
but it is of stair case type.

8. ADVANTAGES OF NPP
• The importan advantage of NPP is the
increased sensitivity, which leads to
detection limits ranging from 10− 7 to
10− 8 M.

9. 3. DIFFERENTIAL PULSE POLAROGRAPHY
• In this technique ,a continuously increasing DC potential is
superimposed with pulse of constant amplitude.
• The pulse is applied only it the end of drop times for
50mS.
• The current is recorded twice during each drop. The
current is recorded just before application of pulse and it
the end of the pulse.
• The difference between these two currents is plotted as a
function of base line potential (E)
• The polarogram obtained consist of a peak instead of a
sigmoidal curve.
• The peak current are the peak height is directly
proportional to the concentration of electroactive species.

10. ADVANTAGES OF DPP
• Non faradaic condenser current is completely
eliminated, residual current become almost zero.
• The total current recorded at the end of the
pulse hence, the only contributor is faradaic
current.
• Detection limit goes down to 10^-8 M.

11. 4. AC POLAROGRAPHY
• In this technique, a continuously increasing DC
potential (E) superimposed with a constant
amplitude AC potential.
• When such combination is applied to DME,
two types of current are generated at DME.
• The total current is the resultant of DC and AC
current.
• The AC component is electronically rectified
and plotted as a function of applied DC
potential (E).

12. ADVANTAGES OF ACP
• Detection limit of the order of 10^-6 to 10^-8 M
can be achieved.
• There is no need of purging nitrogen gas to
remove oxygen because AC polarography is
insensitive to irreversible process like oxygen
reduction.

13. 5. SQUARE WAVE POLAROGRAPHY
• Large amplitude differential technique .
• The waves form applied to the working electrode is a
symmetric square wave superimposed on a base stair case
potential.
• Current is sample twice during each square wave cycle.
• One at the end of forward pulse i1 and one of the end of the
reverse pulse i2 . This result in square wave modulation.
• Modulation amplitude is very large.
• Reverse pulses Couse the reverse reaction of any product
formed from the forward pulse.
• The net current (i1-i2) is the plotted verses the base staircase
potential.
• This gives the peak shape polaogram.
• Peak current is proportional to the concentration of the
analyte.
• The net current is larger then the forward or the reverse
currents.

14. ADVANTAGES OF SWP
• Higher sensitivity then differential pulse in which
reversed current is not used
• Detection limit is up to 10^-8 M.
• Reduced analysis time due to higher scan rates.

15. QUESTIONS?

16. THANK YOU