Titration biamperometric

Polarisation titrations are often referred to as amper-ometric or biamperometric titrations. It is necessary that one of the substances involved in the titration reaction be oxidisable or reducible at the working electrode surface. In general, the polarisation titration method is applicable to oxidation-reduction, precipitation and complex-ation titrations. Relatively few applications involving acid/base titration are found. Amperometric titrations can be applied in the determination of analyte solutions as low as ICE5 M to 10-6 M in concentration. 

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)... 

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

Direct treatment of the whole cream with 2 M hydrochloric acid by refluxing for 30 minutes followed by filtration results in isolation of sulfadiazine. The sulfonamide present in the filtrate is determined by biamperometric titration (24). 

Biamperometric titrations involve the use of two redox electrodes in solution, and are applicable only to titrations where there is a reversible system before or after the endpoint there is no reference electrode. The application of a potential difference causes one electrode to be anode and the other cathode. A current passes due to oxidation or reduction, respectively, of a species present in solution, decreasing to / = 0 at the equivalence point alternatively it may be that 7 = 0 until the equivalence... 

Figure 28 Amperometric titrations with two polarised electrodes (biamperometric titrations).

Biamperometric titrations carried out on modern equipment usually involve stirred solutions, with the current versus volume of titrant being recorded continuously. 8uch titrations usually provide a dead-stop endpoint location. 

The rate of addition of titrant should never be excessive, and this of course applies to biamperometric titrations carried out under continuous current/titrant volume recording. For example, there are titrations where bromine is generated as the titrant to brominate an unsaturated organic as analyte. Too rapid a generation of the bromine depolarizer relative to the speed of bromination can prematurely trigger an endpoint indication where the titration has been set to dead-stop at a specific current value. 

The following are examples of analytes and analytical data, pertaining to foods or pharmaceuticals only, that are determinable by amperometric and biamperometric titrations. 

Of these, water is perhaps by far the substance most determined in foods by biamperometric titration. The determination of water is perhaps worthy of a more complete coverage. The determination is based on the titrimetric procedure developed by Fischer [87] in 1935. His procedure involved the preparation of a titrating reagent consisting of a mixture of iodine, sulphur dioxide and pyridine in methanol. The titration reaction with water involves a two-stage reaction ... 

Figure 29 Biamperometric titration determination of isoniazide in tablets.

C. Pasquini, E.V. Aquino, M.V. Rebougas, F.B. Gonzaga, Robust flow-batch coulo-metric/biamperometric titration system Determination of bromine index and bromine number of petrochemicals, Anal. Chim. Acta 600 (2007) 84. 

Biamperometric titration involves the application of a fixed, usually small, voltage across a pair of identical electrodes. First performed as early as 1897 the technique was rediscovered and applied in 1926. Although the titration curves are not linear, the end point is usually marked by a sharp change in the current. A text ( 44) and a succession of reviews (45) describe the history and subsequent development of these and related titration techniques. 

Nearly all chemical sensors useful for liquid samples can be utiUzed to indicate titrations. Besides the preferred potentiometric, other electrochemical probes are also used, mainly amperometric and conductometric sensors. The so-called biamperometric titration works with simple wire pairs. Photometric and thermometric indication techniques are less common than electrochemical methods. Miniaturization does not play an important role for titration probes. Classical arrangements predominate to this day. Commercial titration instruments are only slowly starting to make use of the achievements of modern sensor technology. As an example, optodes have achieved a certain popularity in recent years for titration applications. 

Note BA biamperometric titration CE-CCD capillary electrophoresis with contactless conductivity detection CL chemiluminescence EB electrochemical biosensor FAAS flame atomic absorption spectrometry FIA flow injection analysis HPLC-UV high-performance liquid chromatography with UV detection MC multicommutation P potentiometry SIA sequential injection analysis SP spectrophotometry TB turbidimetry. 

Biamperometric titration of cyclamate was exploited by Fatibello-Fiho et al. [84,85]. These investigators developed an inexpensive laboratory-built selectable voltage source specially constructed for use in biamperometric titrations. It was made of very simple electronic components and its performance was tested and compared with a potentiostat/galvanostat equipment. The titrant-reagent system was sodium nitrite in 1.0 M phosphoric acid and there was no interference from glucose, fructose, sucrose, lactose, sorbitol, saccharin, benzoic acid, salicylic acid, fumaric acid. Sunset Yellow, and Bordeaux-S. 

Fatibello-Filho, O., M. D. Capelato, and S. A. Calafatti. 1995. Biamperometric titration and flow injection determination of cyclamate in low-calorie products. Analyst 120 2407-2412. 

Fatibello-Fiho, O., I. C. Vieira, S. A. Calafatti, and N. S. M. Curi. 1996. Biamperometric titration of cyclamate of low-calorie products using a selectable voltage source. An. Assoc. Bras. Qutm. 45 131-137. 

Vydra E, Stulik K (1971) Biamperometric titrations (in Czech). SNTL, Prague... 

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