Charge step methods

For decades the electrochemical techniques, i.e., potential, current, or charge step methods such as - chronoamperometry, - chronocoulometry, - chrono-potentiometry, coulostatic techniques were consid-... 

New electroanalytical method coulostatic or charge-step method. Anal. 

Many electrochemical analytical combined methods allow for simultaneous calculation of DC, exchange current (EC), and transfer coefficients. For example, in a method called the coulostatic or charge-step method [28] a current pulse of 0.1-1 ps is applied to the electrode, and the variation of the electrode potential with time after the pulse (that is, at open circuit) is recorded. The method is very similar to GSPM however, the instrumentation is different, namely, the charge is injected by discharging a small capacitor across the electrode. The results are not affected by the double-layer capacity and electrode resistance. 

For decades the electrochemical techniques, i.e., potential, current, or charge step methods such as chronoamperometry, -r chronocoulometry, chrono-potentiometry, coulostatic techniques were considered as fast techniques, and only with other pulse techniques such as temperature jump (T-jump) introduced by Eigen [i] or flash-photolysis method invented by Norrish and Porter [ii], much shorter time ranges became accessible. (For these achievements Eigen, Norrish, and Porter shared the 1964 Nobel Prize.) The advanced versions of flash-photolysis allow to study fast homogeneous reactions, even in the picosecond and femtosecond ranges [hi] (Zewail, A.H., Nobel Prize in Chemistry, 1999). Several other techniques have been elaborated for the study of rapid reactions, e.g., flow techniques (stopped-flow method), ultrasorhc methods, pressure jump, pH-jump, NMR methods. 

Mesoionic compounds (Section 5.07.1.3) are fully aromatic and usually have an exocyclic heteroatom bearing a charge attached to the ring. A new one-step method for converting the exocyclic oxygen of 3-phenyl-l,2,3-thiadiazolium-5-olate 52 into the exocyclic sulfur of 3-phenyl-l,2,3-thiadiazolium-5-thiolate 53 makes use of Lawesson s reagent (Equation 14) <1988BCJ2977>. 

A related technique is the current-step method The current is zero for t < 0, and then a constant current density j is applied for a certain time, and the transient of the overpotential 77(f) is recorded. The correction for the IRq drop is trivial, since I is constant, but the charging of the double layer takes longer than in the potential step method, and is never complete because 77 increases continuously. The superposition of the charge-transfer reaction and double-layer charging creates rather complex boundary conditions for the diffusion equation only for the case of a simple redox reaction and the range of small overpotentials 77 [Pg.177]

Recently, a charge derivatization method was applied (Lee et al., 2004) to successfully analyze small amine molecules in buffer. The compounds to be analyzed were primary and secondary amines including several antibiotics. The amines were mixed with a 10-fold excess of A-hydroxysuccinimidc ester. Although the reaction mixture contained millimolar concentrations of buffer, the mixture was directly analyzed without a desalting step. While noteworthy, this technique adds another tedious step to the analysis, and linearity was limited to a single order of magnitude. 

Troupe and his coworkers reported a two-step method to electrochemically deposit GOx enzyme on a diamond film electrode (Troupe et al. 1998). In the first step, the GOx and BSA were dissolved in a buffer with pH = 7, greater than their isoelectric points. The BDD electrode was immersed into the solution and biased at 3.5 V for 2 h. Therefore, the negatively charged proteins (GOx and BSA) were drawn to the positively charged electrode. In the second step, the glutaraldehyde (GA) cross-links the protein layer forming a water insoluble barrier. 

Auch als Charge-step (60),, .charge-pulse" (71) oder Impulse-Relaxation-Methode (289) bezeichnet. 

The first step in the photocopy process is for the dmm to acquire a uniform static electric charge. The method used is slightly fancier than the... 

Figure 8.7.1 Circuit for charge-step or coulostatic method. In practice, the cell may be held initially at a potential eq by means of a potentiostat that is disconnected immediately before the charge injection.

Charge Step (Coulostatic) Methods 323 For the circuit in Figure 8.7.1, when the relay is in position A, the capacitor,... 

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