Potential scanning detector

Potential of zero charge, 20, 23, 25, 66 Potential scanning detector, 92 Potential step, 7, 42, 60 Potential window, 107, 108 Potentiometry, 2, 140 Potentiometric stripping analysis, 79 Potentiostat, 104, 105 Preconcentrating surfaces, 121 Preconcentration step, 121 Pretreatment, 110, 116 Pulsed amperometric detection, 92 Pulse voltammetry, 67... 

Closed-open systems can also be used for individual and differential kinetic determinations [56,57], a relatively unexplored area In which rapid scan detectors have great potential. 

Gradient scanning is an extension of the gradient dilution in that it uses a dynamic detector, which measures continuously a physical parameter by repeatedly scanning it within a certain range. Originally demonstrated by means of a voltametric detector (current/potential scan [288, 464]), the technique was later extended to spectroscopy [817, 1080] as shown on the emission/wavelength scan in Fig. 2.19. 

In ac cyclic voltammetry, a small amplitude sine wave perturbation is superimposed upon the linear potential scan, and a phase sensitive detector is used to extract and display the in-phase current response as a function of potential. This technique [40-42] is discussed in more detail in Chapter 8, but it is worth noting here that it may have some advantage for the study of fast coupled chemical reactions. At the present stage it is, however, a technique for obtaining numerical parameters when the mechanism is known and there is little in the literature concerning its use as a tool to investigate complex mechanisms. 

LCEC is a special case of hydrodynamic chronoamperometry (measuring current as a function of time at a fixed electrode potential in a flowing or stirred solution). In order to fully understand the operation of electrochemical detectors, it is necessary to also appreciate hydrodynamic voltammetry. Hydrodynamic voltammetry, from which amperometry is derived, is a steady-state technique in which the electrode potential is scanned while the solution is stirred and the current is plotted as a function of the potential. Idealized hydrodynamic voltammograms (HDVs) for the case of electrolyte solution (mobile phase) alone and with an oxidizable species added are shown in Fig. 9. The HDV of a compound begins at a potential where the compound is not electroactive and therefore no faradaic current occurs, goes through a region... 

The ions introduced into the trap are maintained on stable orbits applying DC and RF potential to the electrodes. To separate ions, according to their m/z, a RF scan is made. While the RF amplitude increases, ions with higher m/z values are destabilized and they leave the ion trap moving towards the detector. 

Considerable improvement over film detection can be obtained with either a slow scan CCD camera interfaced to a TEM or with imaging plates. The CCD camera attached to a YAG crystal can have a good linearity in intensity detection, however can present several drawbacks one is the presence of overflow artifacts when ED is recorded, but even more serious problem can be the potential damage of the CCD detector after continuous exposures to high diffracted ED beam intensities. 

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