Deposition step, stripping analysis

Essentially, stripping analysis is a two-step technique. The first, or deposition, step involves die electrolytic deposition of a small portion of the metal ions hi solution into die mercury electrode to preconcentrate the metals. This is followed by die shipping step (the measurement step), which involves die dissolution (shipping) of die deposit. Different versions of stripping analysis can be employed, depending upon die nature of the deposition and measurement steps. 

Potentiometric stripping analysis (PSA) is another attractive version of stripping analysis [7]. The preconcentration step in PSA is the same as for ASV that is, the metal is electrolytically deposited (via reduction) onto the mercury electrode (usually a film). The stripping, however, is done by chemical oxidation, for example, with oxygen or mercuric ions present in the solution ... 

Town, R.M. (1999) Effects of complexants and surfactants on the deposition and stripping steps in chronopotentiometric stripping analysis and anodic stripping voltammetry implications for speciation measurements. Fresenius J. Anal. Chem., 363, 474—476. 

This is concerned almost entirely with trace metal analysis, although a few other applications are known. Metal ions lend themselves particularly well to stripping voltammetry. The metal deposited in the deposition step generally dissolves in the mercury drop to form an amalgam. This avoids any problem with the nature of an insoluble... 

Fig. 62. Scheme of potential-time and current-time dependences in anodic stripping analysis, (a) Ed potential during the deposition period E 1/2 and E"/2 half-wave potentials of two test substances, Ef the final potential t p rest period, tj stripping period. (B) Current-time dependence during the LSV stripping step, IJ, and I" peak heights of the test substances. 

Potentiometric stripping analysis (PSA) is another commonly used technique in water analysis. This technique can usually be applied directly to the analysis of water samples without previous treatment, and it is virtually free from interferences of dissolved oxygen. Both, PSA and ASV techniques are based on the same principle the anal) e is first deposited on the electrode surface while the solution is stirred, and then stripped back to the solution in the measurement step [14,22,196]. The ASV technique works on a film electrode (electrochemically deposited mercury or gold on a glassy carbon support). One advantage of PSA is that it requires simpler equipment than ASV, and can compete with nonelectroanalytical techniques in terms of price, and possibility of automation [247-249]. This method has been applied to determine metals in tap water and rainwater samples [250-253], coupled with FIA to determine copper in natural waters [254,255], etc. In addition, portable PSA instruments have also been developed, and demonstrated to be useful for metals determination in aquatic samples [256-259]. 

Ultrasound assistance can be provided before and (or) during analysis. In those techniques which do not involve any electron exchange at the solution-electrode interface, US is normally applied prior to analysis in order to activate the electrode surface and hence in the absence of sample in electron-exchange processes, US can be applied as a pretreatment, but also during analysis. In the latter case, US can be applied during the measurement step and, in stripping techniques, during deposition of the analyte of interest on the electrode, either electrochemically or by physisorption. 

The potential chosen allows a degree of selectivity. In the analysis of a solution containing a number of metal ions, each metal ion will have its own individual deposition potential. Thus only one metal or a group of metals can be deposited, avoiding the deposition of other metals which might interfere with the stripping step. The higher the potential, the more types of metal etc will be deposited and the more interferences likely. 

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