Square-Wave Polarography

The Model 384B (see Fig. 5.10) offers nine voltammetric techniques square-wave voltammetry, differential-pulse polarography (DPP), normal-pulse polar-ography (NPP), sampled DC polarography, square-wave stripping voltammetry, differential pulse stripping, DC stripping, linear sweep voltammetry (LSV) and cyclic staircase voltammetry. 

Figure 3.16. Waveforms for pulse and differential-pulse polarography. Curves A and D Excitation signal applied to the working electrode. Curves B and E Instantaneous current observed at a single drop as a function of time. Curves C and F The resulting current-versus-voltage curves. In pulse polarography, square-wave voltage pulses of 40-msec duration are applied to the mercury drop, of drop-life mechanically controlled at 2.5 sec (A) ta,ti,ti,... represent successive drops. The overall rate of increase of the amplitude of the voltage pulses is about...

Potential-excitation signals and voltammograms for (a) normal pulse polarography, (b) differential pulse polarography, (c) staircase polarography, and (d) square-wave polarography. See text for an explanation of the symbols. Current is sampled at the time intervals indicated by the solid circles ( ). 

The method of potentiostatic pulses is sometimes combined with the DME (called pulse polarography). hi this case the pulse frequency should match the drop frequency, where each pulse is used at a definite time in the drop life, hi Barker s method, large pulse amphrndes are used. Other versions of the potentiostatic pulse technique are square-wave and staircase voltammetry here smaU-amphtude pulses are used. 

Polarography with superimposed AC signal. As examples of chemical analytical importance we shall consider (a) sinusoidal AC, (b) AC bridge, (c) square-wave and (d) Kalousek polarography. 

Some other less important types of AC polarography may also be considered as sinusoidal ac techniques, as their theoretical treatment can be based on signals from a complex Fourier function in this context we confine ourselves to mentioning sawtooth or triangular wave48 superimposed on the dc ramp. Square-wave polarography is also of that type, but in view of its greater importance we shall treat it separately. 

Fig. 3.47 is comparable to Fig. 3.41 for sinusoidal ac polarography if the tilted shape provides a net compensation of the charging current one obtains a symmetric bell-shaped curve of I in the square-wave polarogram, similar to that depicted in Fig. 3.42. In fact, virtually all of the statements made before on the sinusoidal technique are valid for the square-wave mode except for the rigid shape of its wave this conclusion is according to expectation, especially as Fourier analysis reveals the square wave to be a summation of a series of only...

In connection with the square-wave technique, mention can be made of high-frequency polarography, also called radiofrequency polarography and developed by Barker53, in which a sinusoidal radio-frequency cu, (100kHz to 6.4 MHz) square-wave modulated at co2 (225 Hz) is superimposed on to the dc potential ramp as the wave form includes (apart from additional higher... 

In a method described by Yoshimura and Uzawa [ 144], cadmium in seawater is coprecipitated with zirconium hydroxide (Zr(OH)4) prior to determination by square-wave polarography. The precipitate is dissolved in hydrochloric acid, and cadmium concentration is determined from the peak height of the... 

Cadmium Co-precipitation with zirconium hydroxide, dissolution of Square wave polarography at precipitate in hydrochloric acid -0.6 V [144]... 

To appreciate how the analytical sensitivity of polarography and voltammetry can be enhanced by sampling the current, or by pulsing the potential in normal pulse, differential pulse and square-wave pulse methods to attain a lower concentration limit of about 10 mol dm. ... 

Electrochemical Simulation Package (ESP) is a free program which allows a PC to simulate virtually any mechanism by the following pulse techniques, i.e. cyclic voltammetry, square-wave voltammetry, chronoamperometry and sample DC polarography. The program can also be used in conjunction for fitting experimental data at solid and DME electrodes. It is the only package to explicitly claim to be bug-free . 

From Square-Wave Polarography to Modern Square-Wave Voltammetry... 

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