Importance sampling, electrode-electrolyte

Fig. 8 Top variation of the average surface charge a) = Q)/A with potential, for a supercapacitor composed of a l-butyl-3-methylimidazolium hexafluorophosphate ionic liquid electrolyte and graphite electrodes. The points are raw data extracted from CGMD simulations while the lines are different polynomial fits of the data. Bottom Surfacic differential capacitance, which is either calculated by differentiating a = f(A ) (the colors match with the top panel plots), or from the fluctuations of the charge, using importance sampling methods (WHAM). °...

Another important bioanalytical application of voltammetric ISEs is the detection of polyions (see also above). A technique using cyclic voltammetry on micropipette electrodes filled with the organic electrolyte solutions in 1,2-dichloroethane was successfully applied for the detection of protamine [65] in saline solution and heparin in undiluted sheep plasma samples [66]. Protamine transport was facilitated with dino-nylnaphthalenesulfonic acid (DNNS). As a heparin-selective component the tetrakis-(4-chlorophenyl)borate salt of trimethyloctadecyl ammonium was used. 

Because the electrical circuit is closed inside the sensor, no external reference electrode is necessary and the Severinghaus-type electrode can be used for measurement in either gaseous or liquid samples. It is important to remember, however, that the potential of the internal reference electrode must remain constant. In principle, it would be possible to use a liquid junction but it would add to the complexity of the design. Because the counterion resulting from the dissociation equilibrium is the only interfering ion, and because it is present in a very low concentration, it is possible to ascertain the constancy of the reference potential by careful choice of the internal electrolyte. Thus, for example, in the CO2 electrode the internal electrolyte is O.lMNaHCOs and 0.1 M NaCl and Ag/AgCl is used as an internal reference element. 

In an analytical measurement that employs an ion-specific-electrode, the filling electrolyte should not contain the ion being measured in the sample, or an ion that produces a significant interference at the sensing electrode. This rule is particularly important in trace determinations on small-volume samples where contamination of the sample by the filling solution may be significant. 

Evidence of the electrical conductivity of DNA and of its important mechanisms has been discussed for a long time and has led to a theory of electron conduction in biopolymers [25, 82]. From this it appeared that the major carrier of conductivity is either electronic or ionic, depending on the temperature of the sample, the water content, and the fact that the conductivity of native samples is higher than that of denatured samples. Following electrochemical oxidation of dsDNA and ssDNA in electrolyte solutions over a wide range of pH, interesting electrochemical properties of a glassy carbon electrode with dsDNA or ssDNA adsorbed on the electrode surface were observed [68]. 

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