Square-wave frequency

Chemostat kinetics Weighted divergence as a function of square wave frequency for eft) at the grid point (1, 0 20). 

Fig. 3.11 Dependence of the net peak current of adriamycin (a) and the ratio between the net peak current and frequency (b) on the square-wave frequency. Experimental conditions are as in Figure 3.10 (reprinted from [190] with permission)...

In these equations, Ej represents the electrode potential during the yth half period, 5 the fraction of the square-wave half period at which the current is measured, / is the square-wave frequency (equal to the inverse of the square-wave period), and the other symbols have their customary meaning. As long as the square-wave amplitude, Esw, is lower than 0.5RT jnF—a condition easily accomplished under the usual experimental conditions—the differential sum of the currents flowing during the anodic and cathodic half cycles can be represented by an expression such as [184]... 

The major advantage of square-wave voltammetry is its speed. The effective scan rate is given by / AEs. The term / is the square-wave frequency (in Hz) and AEs is the step height. Frequencies of 1-100 cycles per second permit the use of extremely fast potential scan rates. For example, if AEs = 10 mV and /= 50 Hz, then the effective scan rate is 0.5 V/s. As a result, the analysis time is drastically reduced a complete voltammogram can be recorded within a few... 

Electrochemical data recorded under no steady-state conditions can also be used for studying electrocatalytic processes involving porous materials. In cases where the catalytic system can be approached by homogeneous electrocatalysis in solution phase, variation of cyclic voltammetric profiles with potential scan rate (Nicholson and Shain, 1964) and/or, for instance, square-wave voltammetric responses with square-wave frequency (O Dea et al., 1981 O Dea and Osteryoung, 1993 Lovric, 2002) can be used. This situation can, in principle, be taken for highly porous materials where substrate transport, as well as charge-balancing ion transport, is allowed. On first examination, the catalytic process can be approached in the same manner... 

FIGURE 4.6 Variation of the peak current with the square-wave frequency for deposits on graphite of microparticles of zeolite Y having attached 2,4,6-triphenylthiopyrylium ion (TPYA upon immersion into 0.10 M 111 N( ()/Mei N. 

The Cu-+ to Cu reduction, however, appears as a relatively complicated process, as denoted by peak splitting observed in square-wave voltammetric experiments, as shown in Figure 5.7. Here, peak splitting features are significantly sensitive to variations in the square-wave frequency (i.e., in the timescale) of the voltammetric experiment, thus denoting that different electrochemical pathways are probably involved. 

Separation of the cathodic and anodic components of the net current (measured at the end of forward and backward pulses) in square-wave voltammetries (SQWVs) provided only anodic components for PTA Y electrodes immersed into BU4NPI ),/ MeCN, as depicted in Figure 8.15. In contrast, SQWVs display well-developed anodic and cathodic components for PTA Y electrodes in contact with LiClO4/ MeCN. This feature, indicative of reversible electron transfer processes, was found to be more pronounced on decreasing square-wave frequency. 

Figure 7.3.13 helps to define the principal parameters. The square wave is characterized by a pulse height, A p, measured with respect to the corresponding tread of the staircase, and a pulse width Alternatively, the pulse width can be expressed in terms of the square wave frequency, / == l/2 p. The staircase shifts by A s at the beginning of each cycle thus the scan rate v = = /AjFs- The scan begins at an initial potential,... 

At low square wave frequencies, sampling extends deep into the reaction region, but at high frequencies the depleted region supplies a larger proportion of the sample. This interpretation was supported by experiments in which the gate voltage was varied. ... 

The relationship between the stripping peak current of a fast and reversible mixed reaction and the square-wave frequency is a curve defined by Atp = 0, for/= 0, and an asympfofe A/p = + z [90]. The intercept z depends on the delay time and... 

SWV is characterized by four parameters square wave period, t, pulse width, tp = r/2, step height, AEg, and pulse height, AEsw The pulse width is related to the square wave frequency, / = ll 2tp) and as the staircase step at the beginning of each cycle is AEg, it means that the effective scan rate is u = A s/2fp = fAEg. 

Fig. S (a) liiustration of the operation of the seif-referencing glucose microsensor. A personal computer precisely controls the translational square wave frequency of sensor positioning allowing lonView software to report current changes referred to sensor movements in a gradient. The positioning of the sensor and its motion relative to the target site of interest is guided by observation with a video camera and a monitor.

In the self-referencing mode, the microelectrode is laterally osdllated between two points 5-20 pm apart at a square wave frequency of 0.1-0.3 Hz and data are collected at 100 Hz. The system setup and data processing are illustrated in Fig. 5 [15-19]. Data are reported as differences of voltage or current at two positions. The convention of the difference value is defined as [(V, inear) — (T, ifar)]. where (T, inear) and (V, ifaj.) are the voltages or the currents at the near and far pole, respectively, from the cell. The difference values are directly related to fluxes, which is discussed later. 

Effect of Square Wave Frequency on Current Efficiency in the ... 

However the complex scheme for sampling and reading out the current signal depended on the square-wave frequency of 225 Hz. 

Square wave amplitude l/square wave frequency... 

Figure 20.15. PA spectra of the same sample used for Figure 20.11 when measured with a 100-Hz square-wave. The spectra are shown at the odd harmonics of the 100-Hz square-wave frequency. (Reproduced from [14], by permission of the Society for Applied Spectroscopy copyright 1997.)...

The relationship between the stripping peak current of a fast and reversible mixed reaction and the square-wave frequency is a curve defined by Aip = 0, for /= 0, and an asymptote Aip = fc/+ z [90]. The intercept z depends on the delay time and apparently vanishes when t eiay > s. Consequently, the ratio Aip// may not be constant for all frequencies. This effect is caused by the additional adsorption during the first period of the stripping scan. The stripping peak potential of a reversible mixed reaction depends linearly on the logarithm of frequency [89] ... 

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