Variations of the Conventional Polarographic Method

Many modifications of polarography have been proposed for a number of specific purposes to investigate mechanisms of electrode reactions, to decrease the time needed for examination of a given sample, to increase sensitivity (usually by decreasing the residual or charging current), and so on. Here, those modifications that have found significant applications in analytical work will be briefly described. 

By measuring the difference in current before the application of the voltage pulse and towards the end of the pulse, the charging current contribution is further reduced in magnitude. 

The peak shape of differential-pulse polarograms results from the relation 

Both techniques produce signals that are a linear function of concentration provided that the characteristics of the capillary electrode and the pattern of pulses remain constant. The use of differential pulse assumes constant amplitude of the pulse as well as constant frequency, pulse duration, and location of sampling periods. 

The detection limit for pulse polarography is typically about lO Jl/, and about 10 Mfor the differential-pulse method—although, of course, detection limits do depend on the electrochemical properties of the substance analyzed, interferences, and other experimental variables. The detection limit for arsenic(III) by differential-pulse polarography, for example, has been reported to be 4 x 10 M (0.3 ppb), with a linear calibration curve up to 8 x 10 M. 

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