Twin-polarized microelectrodes

Amperometric titrations with twin-polarized microelectrodes (biamperometric... 

Hi) Amperometric titrations with twin-polarized microelectrodes (or Biamperometric Titrations or Dead-stop-end-point method). 

AMPEROMETRIC TITRATIONS WITH TWIN-POLARIZED MICROELECTRODES (BIAMPEROMETRIC TITRATIONS OR DEAD-STOP-END-POINT METHOD)... 

Figure 17.4 Diagram of Amperometric Titrations With Twin-Polarized Microelectrodes.

Part—III exclusively treats Electrochemical Methods invariably and extensively used in the analysis of pharmaceutical substances in the Official Compendia. Two important methods, namely potentiometric methods (Chapter 16) deal with various types of reference electrodes and indicator electrodes, automatic titrator besides typical examples of nitrazepam, allopurinol and clonidine hydrochloride. Amperometric methods (Chapter 17) comprise of titrations involving dropping-mercury electrode, rotating—platinum electrode and twin-polarized microelectrodes (i.e., dead-stop-end-point method). 

Amperometric Titrations with Twin-Polarized Microelectrodes (Biamperometric Titrations or Dead-Stop-End-Point Method)... 

Twin polarized platinum microelectrodes are conveniently used for endpoint detection for oxidation-reduction titrations. Consider a titration curve for oxidation-reduction titration where both reactants behave reversibly at the electrodes. An example of this kind of titration is titration of iron(II) with cerium(IV) (Fig. 14A). At the starting point of the titration, no current is observed because no suitable cathode reactant is available. With addition of cerium(IV), a mixture of iron(II) and iron(III) is produced, which permits the passage of current. Beyond the midpoint in the titration, iron(III) becomes in excess, and the current is then regulated by decreasing iron(II) concentration. At the equivalence point, the current approaches zero because iron(III) are present, and the applied potential is not great enough to cause these to react at the electrode. Beyond the equivalence point, the current rises again because both cerium(III) and cerium(IV) are present to react at the electrodes. 

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