Titrimetry potentiometric

See also Titrimetry Potentiometric. Water Analysis Seawater - Dissolved Organic Carbon. 

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See also Buffer Solutions. Extraction Solvent Extraction Principles. Indicators Acid-Base. Ion-Selective Electrodes Glass. Sensors Ovenriew. Quality Assurance Internal Standards. Titrimetry Potentiometric. 

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Initial attempts at developing precipitation titration methods were limited by a poor end point signal. Finding the end point by looking for the first addition of titrant that does not yield additional precipitate is cumbersome at best. The feasibility of precipitation titrimetry improved with the development of visual indicators and potentiometric ion-selective electrodes. 

The following experiments may he used to illustrate the application of titrimetry to quantitative, qtmlitative, or characterization problems. Experiments are grouped into four categories based on the type of reaction (acid-base, complexation, redox, and precipitation). A brief description is included with each experiment providing details such as the type of sample analyzed, the method for locating end points, or the analysis of data. Additional experiments emphasizing potentiometric electrodes are found in Chapter 11. 

End Point Determination Adding a mediator solves the problem of maintaining 100% current efficiency, but does not solve the problem of determining when the analyte s electrolysis is complete. Using the same example, once all the Fe + has been oxidized current continues to flow as a result of the oxidation of Ce + and, eventually, the oxidation of 1T20. What is needed is a means of indicating when the oxidation of Fe + is complete. In this respect it is convenient to treat a controlled-current coulometric analysis as if electrolysis of the analyte occurs only as a result of its reaction with the mediator. A reaction between an analyte and a mediator, such as that shown in reaction 11.31, is identical to that encountered in a redox titration. Thus, the same end points that are used in redox titrimetry (see Chapter 9), such as visual indicators, and potentiometric and conductometric measurements, may be used to signal the end point of a controlled-current coulometric analysis. For example, ferroin may be used to provide a visual end point for the Ce -mediated coulometric analysis for Fe +. 

Betti, M., Papoff, R, and Meites, L., Factors Affecting the Precisions of Analyses, by Potentiometric Titrimetry, of Solutions Containing two Weak Acids, Analytica Chimica Acta 182, 1986, 133-145. 

One of the most fruitful uses of potentiometry in analytical chemistry is its application to titrimetry. Prior to this application, most titrations were carried out using colour-change indicators to signal the titration endpoint. A potentiometric titration (or indirect potentiometry) involves measurement of the potential of a suitable indicator electrode as a function of titrant volume. The information provided by a potentiometric titration is not the same as that obtained from a direct potentiometric measurement. As pointed out by Dick [473], there are advantages to potentiometric titration over direct potentiometry, despite the fact that the two techniques very often use the same type of electrodes. Potentiometric titrations provide data that are more reliable than data from titrations that use chemical indicators, but potentiometric titrations are more time-consuming. 

Measurement of Reaction Rates by Titrimetry. The rates of cerium(IV) consumption by each of Cr(C204)3 3, m-Cr(OH2)2(C204)2 and Cr(0H2)4C204+ were also measured by a direct titrimetric method. Solutions were prepared and mixed as for the spectrophotometric procedure. At appropriate times aliquots of the reactant solutions were quenched with known volumes of standard ferrous sulfate, and the excess ferrous ion was titrated potentiometrically with standard potassium dichromate,... 

Precipitation titrimetry — A method for the - titration of species by a - precipitation reaction. Commonly, the - end point of precipitation reactions is monitored by chemical, potentiometric or amperometric methods. A chemical method involves an -> indicator that usually has a change in color at the -> endpoint, while the other methods can be implemented as a -> potentiometric titration or -> amperometric titration, respectively. An important precipitating reagent is silver nitrate, i.e., silver ions Ag+. Such titrations are called argentometric titrations [i], and silver - electrodes are useful as indicator electrodes. 

N. E. de Sousa and O. E. S. Godinho, Simultaneous determination of tartaric, malic and succinic acids by potentiometric titrimetry and its application to wine analysis, Arg. Biol.Tecnol. 33 (4), 903-14 (1990). 

Visual indicators are convenient for rapid precipitation titrimetry with silver ion. Potentiometric end-point detection is also widely used, particularly for dilute solutions, for example, millimolar (see Chapter 14). 

S. F. Simpson and F. J. Holler, Design and Evaluation of a Potentiometric Detection System for Flow Injection Titrimetry. Anal. Chem., 54 (1982) 43. 

Organic compounds may be determined by redox titrimetry, including glucose and other reducing sugars, vitamin C, thiols such as cysteine, and many other organic chemicals of biological importance. There are thousands of potentiometric redox titration methods published in the chemical literature. 

Methods Natural and Artificial Radioactivity Radionuclide Monitoring Radiotracers. Spot Tests. Thin-Layer Chromatography Overview. Titrimetry Oven/iew Potentiometric. X-Ray Fluorescence and Emission X-Ray Fluorescence Theory. 

Static Purge and Trap. Membrane Techniques Dialysis and Reverse Osmosis Ultrafiltration Liquid Membranes. Potentiometric Stripping Analysis. Titrimetry Potent-iometric. 

Titrimetry may also be classified by the nature of the endpoint measurement. The use of electrical measurements gives rise to potentiometric, ampero-metric, and coulometric titrations. Measurement of heat changes is used in thermometric titrimetry, and of absorbance in photometric and turbidimetric titrations. Radiometric titrations measure changes in radioactivity during the titration. All of these techniques are dealt with in other articles in this Encyclopedia. This article discusses only those titrations that use visual indicators. 

A potentiometric titration belongs to chemical methods of analysis in which the endpoint of the titration is monitored with an indicator electrode that records the change of the potential as a function of the amount (usually the volume) of the added titrant of exactly known concentration. Potentiometric titrations are especially versatile because indicator electrodes suitable for the study of almost every chemical reaction used in titrimetry are now available. This technique is also frequently used in the study of operational conditions of visual titrimetric indicators proposed for general use in chemical analysis, as well as in the study of numerous reactions, such as protonation and complexation, which find their application not particularly in analytical measurements. The course of the potentiometric titration curve provides information not only about the titration endpoint position, but also the position and shape of the curve that may provide data about the processes accompanying the titration reaction. Another advantage is that the necessary apparatus is generally less expensive, reliable, and readily available in the laboratories. 

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