Mercury microelectrodes

FIGURE 3. Voltammetric curves at a stationary mercury microelectrode for anthracene in the presence of 17b (a) anthracene alone, 6.5 x 10 3m (b, c, d) previous solution with 2.3, 5.1 and 7.6 x 10"3m of 17b (e) disulphone 17b without anthracene. Medium, DMF-Bu4NC104 0.14m sweep rate, 10mVs 1 (after Reference 25). 

FIGURE 6. Voltammetric curves in DMF-TBAP 0.1 m, stationary mercury microelectrode, sweep rate lOmVs" (1) without phenol, (2)10 m phenol added (a) PhSOjCHjPh, (b) PhSOjC(Et)(Me)Ph. 

FIGURE 11. Cyclic voltammetries of 68 at a mercury microelectrode, concentration 2x10 m, electrolyte OMF/Bu NI 0.1m, reference electrode Ag/Agl/I" 0.1m, sweep rate 300mVs ... 

The dropping mercury microelectrode (DM E) technique was used for the mechanistic study of Cd(II) reduction in aqueous KE [38] and 0.5 M Na2S04 [39] solutions. 

Electroreduction of Cd(II)-nitrilotriace-tic acid and Cd(II)-aspartic acid systems was studied on DME using SWV [73]. The CE mechanism in which the chemical reaction precedes a reversible electron transfer was established. Also, the rate constants of dissociation of the complexes were determined. Esteban and coworkers also studied the cadmium complexes with nitrilotriacetic acid [74, 75] and fulvic acid [76]. The complexation reaction of cadmium by glycine was investigated by different electrochemical methods using HMDE and mercury microelectrode [77, 78]. 

Concerning more general application of mercury electrode in the studies on com-plexation equilibria, one should mention the paper by Jaworski et al. [59], who have investigated oxidation of mercury microelectrode in solutions with thiocyanates without any background electrolyte added. In the experiments, normal pulse voltammetry and staircase voltammetry were used. The authors have developed a general procedure for the determination of the stability constants, based on the data taken from the voltammograms. They have applied it to the analysis of Hg(II)-SCN complexes. 

Daniele, S., B. Salvatore, M.A. Baldo, P. Ugo, and G. Mazzocchin. 1989. Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes. Part 2. Application to rain and sea waters. Anal. Chim. Acta 219 19-26. 

Bond, A.M., Czerwinski, W.A. and Llorente, M. (1998) Comparison of direct current, derivative direct current, pulse and square wave voltammetry at single disc, assembly and composite carbon electrodes stripping voltammetry at thin film mercury microelectrodes with field-based instrumentation. Analyst, 123, 1333-1337. 

For example, as illustrated in Figure 4.4, the cyclic voltammetric behavior of 2-hydroxyanthraquinone (20H-AQ) monolayers on mercury microelectrodes is... 

Figure 4.4 Cyclic voltammograms (continuous lines) obtained for a 20 pm radius mercury microelectrode immersed in a 10 pM solution of 20H-AQ in 1.0 M HCIO4. The scan rates, from top to bottom, are 50, 20, 10 and 5 V s the current scale is on the right-hand side. The dotted line represents the cyclic voltammogram observed for the same electrode immersed in a 10 mM solution of 20H-AQ in this case, the scan rate is 50 V s, with the current scale on the left-hand side. In all cases, cathodic currents are up, and anodic currents are down, with the initial potential being +0.250 V. Reprinted with permission from R.J. Forster, Anal. Chem., 68, 3143 (1996). Copyright (1996) American Chemical Society...

Figure 5.27 Cyclic voltammograms obtained for 30 pm radius mercury microelectrodes immersed in 5 pM solutions of (a) adriamycin and (b) quinizarin. The scan rates are, from top to bottom, 50,20, 10 and 5 V s-1 the supporting electrolyte is 1.0 M HC104. The cathodic currents are shown as up, while the anodic currents are shown as down the initial potential is —0.700 V. From R. J. Forster, Analyst, 121, 733 - 741 (1996). Reproduced by permission of The Royal Society of Chemistry...

As distinct from sohd supports such as gold or silver, mercury imparts lateral mobihty to hpid monolayers directly self-assembled on its surface, because of its liquid state. This is demonstrated by rapid spontaneous phase separation, with microdomain formation, in a hpid mixture monolayer self-assembled on top of a DPTL thiolipid monolayer tethered to a mercury microelectrode [30]. The presence of microdomains was directly verified from the images of the distal hpid monolayer obtained using two-photon fluorescence lifetime imaging microscopy. 

Together with carbon, mercury is one of the most attractive electrode materials. It has high proton reduction overpotential and a very well-defined and smooth surface. For these reasons it has been widely used as electrode material in organic electrochemistry. The preparation of mercury microelectrodes has thus been an interesting and challenging problem that has been addressed by several groups (29-31). The technique of making mercury... 

FIGURE 8. Cyclic voltammetry of the tosylamide shown in DMF/Bu4NI 0.1 M vs Ag/Agl/I 0.1M as a reference. Mercury microelectrode. Sweep rate 0.1 V s l. Curves corresponding to the first sweep (— ) and the second sweep (— — ). (From Reference 37)... 

FIGURE 11. Voltammetric reduction of 1-naphthalenesulphonyl chloride (C 9.7 x 10 3 M) in DMF/Bu4NI. Stationary mercury microelectrode. Curve a 5 sweep rate 0.1 Vs-1. Curve b after controlled potential electrolysis at —1.4 V (arrow) after 1.92 Fmol"1 (total reduction) have passed. Curve c shows the response after adding to the preceding solution an excess of methyl iodide showing the formation of the corresponding sulphone (from Reference 45)... 

Figure 3 Attainable anodic and cathodic potential limits for platinum and mercury microelectrodes. (Reproduced with permission from Ewing GW (1985) Instrumental Methods of Chemical Analysis, 5th edn., p. 290. New York McGraw-Hill.)...

Baldo MA, Bragato C, and Daniele S (1997) Determination of lead and copper in wine by anodic stripping voltammetry with mercury microelectrodes assessment of the influence of sample pretreatment procedures. Analyst 122 1—5. 

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