Differential pulse polarography, also known as differential pulse voltammetry, is a type of voltammetric technique that is quite similar to normal pulse polarography but there are many differences as well. Let’s see the principle, instrument, and advantages of DPP techniques in brief.
Differential pulse polarography principle
In differential pulse polarography, the base potential applied during most of a drop’s lifetime is not constant from drop to drop, but instead, it is changed steadily in small increments. The pulse height is only 10 to 100 mV, usually 50 mV and is maintained at a constant level with respect to the base potential. There are two ways in which the pulse can be applied.
- Pulse on staircase scan: a constantly increasing potential pulse is applied in a staircase manner.
- Pulse on the linear scan: a constant but small amplitude potential pulse is superimposed on a DC potential ramp.
In this technique, two current samples are taken during each drop’s lifetime.
- The first current is measured at the time(T’) immediately before the pulse.
- The second current is measured at the time(T), late in the pulse, and just before the drop is dislodged.
The first current is instrumentally subtracted from the second current and this current difference(Δi) is plotted versus the applied potential, a voltammogram is obtained as shown below.
The resulting differential pulse voltammogram consists of current peaks, the height of which is directly proportional to the concentration of the corresponding analytes. Moreover, the peak potential(Ep) can be used to identify the species because it occurs near the polarographic half-wave potential.
Instrumentation of Differential pulse polarography
The block diagram of the instrumentation of DPP is shown below.
Advantages of differential pulse polarography
The advantages of DPP over NPP and DC polarography are given below.
- DPP provides a greatly improved signal-to-noise ratio compared with NPP.
- The detection limit of DPP(10-8– 10-9M) is better than NPP(10-5).
- It can be employed to study both reversible and irreversible systems.
- It is very effective in multi-analysis.
- It is very useful for the quick analysis of the low concentration of the substance than the other two.