Scan rate analysis

TABLE S3 Diagnostic Parameters Extracted from the Scan Rate Analysis in Figure 5.8. 

Scan rate analysis in G. sulfurreducens biofilms is one of the most often used methods to determine a particular type of electron transfer (i.e., diffusion based). In Figure 5.17a, the CVs obtained at increasing scan rates of 1 up to 100 mV s are shown. The corresponding peak currents are shown in Figure 5.17b. The line... 

Figure 5.17 Scan rate analysis of G. sulfurreducens biofiltns under turnover conditions, (a) CVs at increasing scan rates, (b) Peak currents at each scan rate plotted against the square root of the scan rate.

When we extended the scan rate analysis range from 320 to 1280 mV s for the same G. sulfurreducens biofilm, we observed a peculiar scan rate dependence... 

Figure 5.19 Extended scan rate analysis for the nonturnover CVs in Figure 5.18a. (a) Peak current versus v . (b) Peak current versus v. (c) Peak potential versus (d) AF versus v. The scan rate was increased up to 1280 mV s . ...

Here, we have demonstrated the differences between turnover and nontumover CVs for G. sulfurreducens biofilms. Turnover and nonturnover CVs can be used to correlate catalytic current under turnover conditions to redox peaks under nonturnover conditions. Scan rate analysis can provide a qualitative understanding of the biofilm electron-transfer mechanisms occurring within a biofilm. However, caution should be used when applying the Randles-Sevcik criterion to biofilms, as it was derived for a single-step, reversible electron-transfer step for diffusing mediators. 

Differential pulse voltammetry provides greater voltammetric resolution than simple linear sweep voltammetry. However, again, a longer analysis time results from the more sophisticated potential waveform. At scan rates faster than 50 mV/sec the improved resolution is lost. Because it takes longer to scan the same potential window than by linear sweep, an even longer relaxation time between scans is required for differential pulse voltammetry. 

Figure 12.10 Analysis of SFG spectra from atop CO on Pt(lll) using a CO-saturated 0.1 M H2SO4 electrolyte and a scan rate of 5 mV/s. The (2 x 2) —3CO (- /l9 x - /l9)R23.4°— 13CO phase transition resulted in a jump in atop amplitude (a). Stark tuning (b) and peak width versus electrode potential data (c) are also shown. (Filled circles denote hnear Stark tuning behavior while open circles correspond to deviations from linear behavior during oxidation.)...

An advantage of the microbore gas chromatrography/time-of-flight mass spectrometry (GC/TOFMS) method over the other two approaches is that separation efficiency need not be compromised for speed of analysis. The rapid deconvolution of spectra ( scan rate ) with TOFMS makes it the only MS approach to achieve several data points across a narrow peak in full-scan operation. However, the injection of complex extracts deteriorates performance of microbore columns quickly, and an increased LOD and decreased ruggedness result. Microbore columns may be used in water analysis if the LOD is sufficiently low, but they can rarely be used in real-life applications to complicated extracts. 

Differential Scanning Calorimeter (DSC) thermograms were obtained on a Perkin Elmer DSC-2 run at 10°C per minutes. Dynamic Mechanical Thermal Analysis (DMTA) spectra were obtained on a Polymer Labs DMTA at a frequency of 1Hz with a temperature range from -150°C to +150°C at a scan rate of 5°C per minute. 

Banks [39] later verified Sf as electroactive with quantitative analysis of cyclic voltamtnograms (Fig. 29a,b) in free electrolyte with varying gas composition equilibrated with the melt. From Banks analysis of the distinctive current function dependence on scan rate (Fig. 29c) it was concluded that the cathodic reaction was catalytic in nature ... 

In terms of mechanism analysis, one of the most useful features of the peak current is its proportionality to concentration and, even more important, its proportionality to the square root of the scan rate. The peak potential is independent of scan rate and concentration and provides easy access to the standard potential E° (at 25°C, the peak potential is 28.5 mV more negative than the standard potential). At the same temperature, the peak width is 56.5 mV. Another diagnostic criterion is the distance between the anodic and cathodic peak potentials, 2.22(7ZT/F) (i.e., 57 mV at 25°C). 

The Faradaic and capacitive components of the current both increase with the scan rate. The latter increases faster (proportionally to v) than the former (proportionally to y/v), making the extraction of the Faradaic component from the total current less and less precise as the scan rate increases, particularly if the concentration of the molecules under investigation is small. The variations of the capacitive and Faradaic responses are illustrated in Figure 1.7 with typical values of the various parameters. The analysis above assumed implicitly that the double-layer capacitance is independent of the electrode potential. In fact, this is not strictly true. It may, however, be regarded as a good approximation in most cases, especially when care is taken to limit the overall potential variation to values on the order of half-a-volt.10 13... 

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