Titration radiometric

In radiometric titration, the titrant and/or titrand is labelled. After the reaction and separation of the products e.g. by filtering a precipitate, either or both products are counted. A plot of the count rate against the volume of titrant shows a sudden change of 

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Figure 4.10 Radiometric titration of 110AgNO3 with NaCl.

One of the most popular radiometric techniques is that of radiometric titrations. In a radiometric titration, the unknown is titrated with a radioactive reagent, and the radioactivity of the product or supernate, formed by the chemical reaction of the reagent and the unknown material, is monitored as a function of titrant volume to determine the endpoint. This means that the radioactive component being followed must be isolated during the titration and its activity measured—that is, a discontinuous titration. 

The classic example of a radiometric titration concerns the titration of some unknown material with a radioactive reagent to give a radioactive precipitate. In this case, the activity of the supernatant or the precipitate can be followed as a function of titrant volume, as shown in Figure 4.10. In this type of titrations, the tracer must have a long half-life and must emit high-energy 3 or y rays so as to minimize self-absorption corrections (assuming, as is common practice, that the supernatant or precipitate is removed from the system and counted in an external sample counter after the addition of each volume of titrant). 

Braun, T. and J. Tolgyessy. Radiometric Titrations, Pergamon, Oxford, 1967. 

Braun, T., and J. Tolgyessy Radiometric Titrations. Intern. Series of Monographs on Analytical Chemistry, Vol. 29. Oxford Pergamon Press 1967. 

Addition of radioactive tracers for analytical purposes offers additional possibilities of radioanalysis. By isotopic dilution not only elements, but also compounds, can be determined quantitatively, provided that these compounds are available in labelled form. Radiometric methods comprise application of isotopic exchange, release of radionuclides and radiometric titration. 

In radiometric titration, the radioactivity of one component or in one phase is recorded as a function of addition of titrant. The compound formed is separated by precipitation, extraction or ion exchange in the course of the titration, and the endpoint is determined from the change in the activity in the residual solution. Radio-metric titration may be applied in different ways inactive test solution and active titrant (activity in the solution is low at the beginning and begins to rise at the endpoint) active test solution and inactive titrant (activity in the solution decreases continuously, until the endpoint is reached) both the test solution and the titrant... 

T. Braun and 1. TOloyessy, Radiometric Titrations, Petgamon Press, Oxford, 1967. 

Figure 19.14. Theoretical titration curve for the radiometric titration o/0.001 M Cl with a solution o/0.001 M Ag spiked with °Ag.

Figure 19.15. A simple experimental set-up for radiometric titrations employing precipitation reactions.

Advantages and Limitations of Radiometric Titrations. Radiometric detection of the equivalence point is a general method that does not depend on the chemical reaction employed. This contrasts with other methods of detection, which depend on specific chemical or physical transitions at the equivalence point. Amperometric titrations are applicable only to electrochemically active systems conductometric titrations apply only to ionic solutions, and so on. In principle, any titration system in which a phase separation can be effected is amenable to radiometric detection, provided there exist suitable radioactive labels. The major limitation of the method is the requirement for phase separation. In precipitation titrations, the phase separation is automatic and the method is well suited to this class of titrations. For other classes of titrations, special phase-separation methods, such as solvent extraction, need to be applied. At the present time, the method suffers from a lack of phase-separation techniques suitable for continuous monitoring of the titration curves. 

Braun, T., and TSloyessy, J. Radiometric Titrations. New York Pergamon Press, 1967. This book is the only authoritative book on the subject of radiometric titrations. A detailed and up-to-date account of both theoretical and experimental aspects of this subject is given. 

A 50-ml solution of 1.00 mM Ag is titrated with a 1.0 mAf solution of K2- Cr04 (Half-life = 27.8 days) with an activity of 1.00 x 10 dps/mol. Plot the anticipated radiometric titration curve. 

Radiometric titration usually involves use of radioactive reagents to determine the equivalence point (endpoint) but these are variants that do not use a radio-reagent instead they are based on a... 

Radiometric titrations follow the relation between the radioactivity of one component or phase of the solution under analysis and the volume of added titrant. The compound formed during the titration must be easily separable from the excess of unreacted ions. This separation is directly ensured only in the case of precipitation reactions (Figure 2). In other types of reactions, the separation can be accomplished using an additional procedure. The endpoint is determined from the change in the activity of the residual solution or of the other phase. 

According to the type of chemical reaction used, methods based on the formation of precipitates and methods based on complex formation can be distinguished (Figure 3). Because of the necessity for handling precipitates, precipitation radiometric titrations are difficult to apply to less than milligram amounts and, therefore, have no special advantages... 

The application of radiometric titrations has declined over the past three decades. Their main advantage is where classical methods for detection of the endpoint are either impossible or subject to interference from the titration medium. 

Braun T and Tolgyessy J (1967) Radiometric Titrations. Oxford Pergamon. 

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. 

Radiometric methods other than the isotope dilution analysis are not necessarily versatile. But they provide convenient and reliable technique in certain cases (Braun and Tolgyessy 1967). In radiometric titration, a radioactive indicator is used to monitor the end-point of the titration. For example. Cl ions in an aqueous solution sample are titrated with a standard solution of Ag solution labeled with Ag. Until the equivalence point is attained essentially all the Ag ions are precipitated as AgCl, giving little activity in the supernatant solution. At the equivalence point, the activity begins to increase linearly. Plotting the activity of the solution against the amount of Ag solution added, the equivalence point is clearly determined as the intersection of two fines. This technique is reliable and convenient, if both the separation of the supernatant solution from the precipitate and the activity measurement are made automatically. 

Radiometric titration usually involves use of radioactive reagents to determine the equivalence point, but there are variants that do not use a radioreagent instead they are based on a change in the intensity of radiation caused by its absorption or scattering in a medium containing the analyte [2], [32], [87], [92], [95], [96], [97]. 

According to the type of chemical reaction used, methods based on the formation of precipitates and methods based on complex formation can be distinguished. Because of the necessity for handling precipitates, precipitation radiometric titrations are difficult to apply to less than milligram amounts and. therefore, have no special advantages over other volumetric methods. The sensitivity of complexometric titrations is limited by the sensitivity of the determination of the endpoint. However, the use of radiometric detection can substantially increase the sensitivity of this type of determination. For the separation of the product from the initial component, liquid-liquid distribution, ion-exchange, electrophoresis, or paper chromatography are most often used [2]. [63], [88], [93], [97]. 

Protein binding has been used in various guises as a method for analysis of tannins and tannin-containing extracts. The hide powder method has been used for decades in the leather industry. More recently, methods based on the residual absorbance of unprecipitated hemoglobin (10), radiometric titration with labelled bovine serum albumin (BSA) (51), and the ferric chloride induced color of protein-tannin complexes resolubilized in alkali (50) have all been suggested as methods of tannin analysis. 

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