Complex-formation titrations applications

The main idea of research is application of accessible, simple and express methods that don t need expensive reagent techniques for analysis of phanuaceutical products based on bischofite. The determination of metal ions such as Mg, Zn, Cu, Fe by complex-formation titrations using a widely applicable chelating agent, EDTA, have been studied as a function of pH, complexing agents and indicators. The analysis consists of four parts ... 

In fact, any type of titration can be carried out potentiometrically provided that an indicator electrode is applied whose potential changes markedly at the equivalence point. As the potential is a selective property of both reactants (titrand and titrant), notwithstanding an appreciable influence by the titration medium [aqueous or non-aqueous, with or without an ISA (ionic strength adjuster) or pH buffer, etc.] on that property, potentiometric titration is far more important than conductometric titration. Moreover, the potentiometric method has greater applicability because it is used not only for acid-base, precipitation, complex-formation and displacement titrations, but also for redox titrations. 

Ruzic [278 ] considered the theoretical aspects of the direct titration of copper in seawaters and the information this technique provides regarding copper speciation. The method is based on a graph of the ratio between the free and bound metal concentration versus the free metal concentration. The application of this method, which is based on a 1 1 complex formation model, is discussed with respect to trace metal speciation in natural waters. Procedures for interpretation of experimental results are proposed for those cases in which two types of complexes with different conditional stability constants are formed, or om which the metal is adsorbed on colloidal particles. The advantages of the method in comparison with earlier methods are presented theoretically and illustrated with some experiments on copper (II) in seawater. The limitations of the method are also discussed. 

In organic solvents, the possibility of complex formation appears to be enhanced over that in aqueous solutions. Such equilibria are conveniently studied by means of potentiometric titrations. Although most of the published data for organic systems involve silver halides, the method is quite general and is applicable to any system providing that the concentration of at least one ion can be independently monitored, say by e.m.f. measurements. (Since a detailed analysis of this method has been given by Butler only an outline will be given here.)... 

A study of the complex formation of CB [5] with K ion in neutral water using titration calorimetry showed that CB [5] binds ion in a 1 2 stoichiometry. The utility of water-soluble CB [6J was also illustrated by formation of a stable 1 1 host-guest complex with acetylcholine in neutral water. The good solubilities of CB [5J and CB [6] in organic solvents make then-applications in ion-selective electrodes (ISEs) possible. Membrane electrodes prepared with CB [51 and CB [6J... 

Alkyl sulfonate, sulfate, and fatty amine are usually tested by using dye-reagent complex formation and counter ion titration. The applications of dye-reagent complex formation and counter ion titration are mainly introduced by the following. 

A simple example of the application of a complexation reaction to a titration procedure is the titration of cyanides with silver nitrate solution. When a solution of silver nitrate is added to a solution containing cyanide ions (e.g. an alkali cyanide) a white precipitate is formed when the two liquids first come into contact with one another, but on stirring it re-dissolves owing to the formation of a stable complex cyanide, the alkali salt of which is soluble ... 

Complexation reactions have many uses in analytical chemistiy, but their classical application is in complexometric titrations. Here, a metal ion reacts with a suitable ligand to form a complex, and the equivalence point is determined by an indicator or an appropriate instrumental method. The formation of soluble inorganic complexes is not widely used for titrations, as discussed later, but the formation of precipitates, particularly with silver nitrate as the titrant, is the basis for many important determinations (see Section 13F). 

The most widely used complexometric titration employing a unidentate ligand is the titration of cyanide with silver nitrate, a method introduced by Liebig in the 1850s. This method involves the formation of the soluble Ag(CN)J, as discussed in Feature 17-2. Other common inorganic complexing agents and their applications are listed in Table 17-1. 

Eriochrome Black T forms red complexes with more than two dozen metal ions, but the formation constants of only a few are appropriate for end point detection. As shown in Example 17-5, the applicability of a given indicator for an EDTA titration can be determined from the change in pM in the equivalence-point region, provided that the formation constant for the metal indicator complex is known. ... 

The classical gravimetric determination of iron now finds little application in pharmaceutical work, partly because of the readiness with which other ions are adsorbed on to the precipitate but principally because of the variety of titrimetric methods which are available. Oxidising titrants are the most widely used and these may be applied directly to ferrous iron or, after suitable reduction, to ferric iron. Reducing titrants also find some application for the direct titration of ferric iron. Chelating titrants such as EDTA may be used but, because of the formation of a highly coloured complex and because other rapid titrimetric methods are already available, these are unlikely to find routine application. 

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