Detection systems amperometric type

Through the choice of stationary phase and eluent composition, the selectivity can be modulated, but the eluent must meet the requirements of the detection system. Although the conductivity detector is still the most popular, other types of detection can be applied for different analytes. These include electrochemical (amperometric, pulsed and integrated amperometric, potentiometric), photometric (UV-Vis, indirect photometric following post column derivatisation, chemiluminescence, refractive index), and fluorescence. 

In acid-base titrations the end point is generally detected by a pH-sensitive indicator. In the EDTA titration a metal ion-sensitive indicator (abbreviated, to metal indicator or metal-ion indicator) is often employed to detect changes of pM. Such indicators (which contain types of chelate groupings and generally possess resonance systems typical of dyestuffs) form complexes with specific metal ions, which differ in colour from the free indicator and produce a sudden colour change at the equivalence point. The end point of the titration can also be evaluated by other methods including potentiometric, amperometric, and spectrophotometric techniques. 

S. Sawada, H. Torii, T. Osakai, and T. Kimoto, Pulse amperometric detection of lithium in artificial serum using a flow injection system with a liquid/liquid-type ion-selective electrode. Anal. Chem. 70, 4286-4290 (1998). 

One of the benefits of electrochemical batch injection analysis is that dilution of the sample with electrolyte is not necessary, see below. A sample of volume =sl00p.L is injected directly from a micropipette, tip diameter 0.5 mm, over the centre of a macroelectrode exactly as in a wall-jet system. This is equivalent to a flow injection system with zero dispersion. During the injection, and after a short initial period to reach steady-state, the hydrodynamics is wall-jet type and a time-independent current is registered. BIA was first devised using amperometric, e.g., [31], and potentiometric, e.g., [34], detection. A typical amperometric trace is shown in Fig. 16.5. By using a programmable, motorised electronic... 

The tips discussed so far have been amperometric probes, typically of Pt-Ir, that produce faradaic currents reflecting redox processes at an exposed surface. However, it is also possible to use potentiometric tips, such as ion selective electrodes based on micropipets, in an SECM (28, 29). These produce potentials (with respect to a reference electrode) that depend logarithmically on the solution activity of a specific ion. Tips of this type that can detect H, Zn, NH4, and with a resolution of a few pirn have been described. Tips of this type are especially useful for detection of nonelectroactive ions, like many of those of interest in biological systems. However, such tips are passive probes, in that they detect the local activity of a given species but do not sense the presence of the substrate. They cannot be used to determine d, so they must be positioned with respect to a substrate, such as, in studying a concentration gradient at an electrode, by visual observation with a microscope, by resistance measurements, or by using a double-barrel tip that contains both an amperometric element and a potentiometric one. 

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