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Differential Pulse Polarography (DPP)


Differential Pulse Polarography is a polarographic technique that uses a series of discrete potential steps rather than a linear potential ramp to obtain the experimental polarogram. Many of the experimental parameters for differential pulse polarography are the same as with normal pulse polarography (for example accurately timed drop lifetimes, potential step duration of 50 - 100 ms at the end of the drop lifetime). Unlike Normal Pulse Polarography, however, each potential step has the same amplitude, and the return potential after each pulse is slightly negative of the potential prior to the step.

Differential pulse polarography

In this manner, the total waveform applied to the DME is very much like a combination of a linear ramp with a superimposed square wave. The differential pulse polarogram is obtained by measuring the current immediately before the potential step, and then again just before the end of the drop lifetime. The analytical current in this case is the difference between the current at the end of the step and the current before the step (the differential current). This differential current is then plotted vs. the average potential (average of the potential before the step and the step potential) to obtain the differential pulse polarogram. Because this is a differential current, the polarogram in many respects is like the differential of the sigmoidal normal pulse polarogram. As a result, the differential pulse polarogram is peak shaped.

Differential pulse polarography has even better ability to discriminate against capacitive current because it measures a difference current (helping to subtract any residual capacitive current that remains prior to each step). Limits of detection with Differential Pulse Polarography are 10-8 - 10-9 M.

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