Stripping voltammetry techniques experiment

Sensitivity In many voltammetric experiments, sensitivity can be improved by adjusting the experimental conditions. For example, in stripping voltammetry, sensitivity is improved by increasing the deposition time, by increasing the rate of the linear potential scan, or by using a differential-pulse technique. One reason for the popularity of potential pulse techniques is an increase in current relative to that obtained with a linear potential scan. 

In the previous chapter, we encountered a form of coulometry known as stripping . We can combine both stripping and voltammetry in the powerful technique of stripping voltammetry. As we have seen, the potential of the working electrode is ramped during a voltammetric or polarographic experiment. The resultant current represents the rate at which electroactive analyte reaches the surface of the electrode, that is, current / a flux j. 

The use of pulse techniques for electroanalytical determinations has been much publicized, and is applicable to both solid electrodes and the HMDE/SMDE. The development in recent years of square wave voltammetry (SWV)39 widens the possibilities beause of its rapidity (Section 10.9) it is especially useful because the time necessary to do an experiment is only 2 s, which means that a SMDE drop in the dropping mode can also be used for micromolar determinations. Progress obtained with pulse techniques40,41 has meant that applications of a.c. voltammetry have been few, but there is no theoretical reason for this. The very low detection limits achieved in stripping voltammetry result not only from the pre-concentration step but also from the use of pulse waveforms in the determination step. 

Another variation involves the stripping or electrolysis of species that have spontaneously adsorbed on the surface of an electrode without the preelectrolysis step. This technique, called adsorptive stripping voltammetry, can be applied, for example, to sulfur-containing species, organic compounds, and certain metal chelates that adsorb on Hg and Au (74, 81). Examples include cysteine (and proteins that contain this amino acid), dissolved titanium in the presence of the chelator solochrome violet RS, and the drug diazepam. The amounts found by this method would necessarily be limited to monolayer levels. However, similar approaches can be employed with thicker polymer layers that can interact with solution species. Related experiments are described in Chapter 14. 

Studies made with this instrumentation on other voltammetrlc techniques such as anodic stripping voltammetry allow one to conclude that the optimization of initial d.c. linear sweep or stripping data leads to optimum performance In the semi-integral, semi-differential and derivative approaches and that, under Instrumental equivalent conditions where d.c. experiments have been optimized with respect to electronic noise and background correction, detection limits are not markedly different within the sub-set of related approaches. Obviously, the resolution and ease of use of a method providing a peak-type readout (semi-differential) are superior to those with sigmoidally shaped read- outs (semi-integral). 

Anodic Stripping Voltammetry (ASV) is an extremely sensitive electro-analytical technique that can determine trace quantities of certain metals at the parts-per-billion level. The first phase of an ASV experiment involves a pre-concentration... 

Voltammetry was described briefly in the previous chapter, when we first looked at stripping techniques. To recap during the experiment, the potential is ramped from an initial value, E, to a final value, Ef (see Figure 6.5). The potential of the working electrode is ramped, with the rate of dE/dr being known as the sweep rate, i. The sweep rate is also called the scan rate. Note that the value of v is always cited as a positive number. 

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