Mercury ionic strength dependence

The oxidation of guanine (G) and adenine (A) follows a two-step mechanism involving the total loss of four electrons and four protons showing current peaks at approximately 0.9 and 1.2 V, respectively. However, the redox properties are dependent on the pH, the ionic strength of the electrolyte, and the electrode material.2 The reader is referred to a recent review by Palecek and coworkers for a more comprehensive discussion regarding the electrochemical mechanism of the oxidation and reduction of DNA bases on carbon and mercury electrodes.3 4 Guanine oxidation is irreversible and occurs in two consecutive steps (Fig 10.1).5... 

It is important to note that proteins tend to denature during such an adsorption process on noble metals or carbon electrodes. In addition, the stability of the adsorbed sensing layer is highly dependent on the pH value and ionic strength of the solution as well as the temperature, the electrode material, and other additional factors. For instance, as early as 1972 direct ET was observed on mercury electrodes employing cytochrome c as redox protein [108]. Reversible electrochemical behavior of cytochrome c was not observed because the protein denatured on the surface. 

Figure 3. Comparison of the concentration dependence of added photosensitizer on the photodegradation rate of methionine. For each case the solutions were 5 yM in methionine and were Irradiated for 2 hours using only wavelengths > 3U0 nm Isolated from a mercury medium pressure lamp. All samples were prepared In air saturated artificial seawater of ionic strength 0.7 and with pH of 8.1.

As discussed by Tercier and Buffle [116], when trying to carry out ASV in samples of low or variable ionic strength, it can be difficult to correlate peak heights and analyte concentration. This difficulty arises because counterion transport is coupled to oxidation of the metal that is concentrated within the mercury or polymeric film. Therefore, the peak height, width, and position can depend significantly on the identity and concenhation of the counterions in the sample. 

The studies on the adsorption of model compounds, synthetic polynucleotides and degradation products of nucleic acids with the aid of a.c. polarography [98-101] indicate that all three basic constituents of nucleic acids, i.e., bases, sugars and phoshoric acid participate in the adsorption of nucleic acids at mercury electrodes. The extent of their participation in the adsorption of nucleic acids depends on their secondary structure in the bulk of solution, ionic strength and pH of the medium and the magnitude and sign of the surface charge [99, 102]. 

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