Continuous variation method

It has been established, that both DN and Ibp form complex compounds with ions Eu(III), Sm(III), Tb(III) and Dy(III), possessing luminescent properties. The most intensive luminescence is observed for complex compounds with ion Tb(III). It has been shown, that complexation has place in low acidic and neutral water solutions at pH 6,4-7,0. From the data of luminescence intensity for the complex the ratio of component Tb Fig was established equal to 1 2 by the continuous variations method. Presence at a solution of organic bases 2,2 -bipyridil, (Bipy) and 1,10-phenanthroline (Phen) causes the analytical signal amplification up to 250 (75) times as a result of the Bipy (Phen) inclusion in inner coordination sphere and formation of different ligands complexes with component ratio Tb Fig Bipy (Phen) = 1 2 1. 

Information on the stoichiometry of a complex can also be obtained from the continuous variation method (see Connors, 1987). Let us consider a complex MmL formed according to the equilibrium... 

He found the method for the determination of the composition of unstable coordination compounds formed in solution in 1921 [1], which was later proposed by P. Job [2] and is known as the continuous variation method or Job s method. Shibata s discovery of the method was much prior than that of Job, but it was not well recognized by chemists around the world, because his report was written in Japanese. He was the Dean of the Faculty of Science of Nagoya University, and then, the President of the Tokyo Metropolitan University. He was appointed to be the President of Japan Academy. 

Continued polymerization/depolymerization, PROCESSIVITY Continuous variation method,... 

Khalil et al. [51] described the microquantitative determination of mefenamic acid based on the reaction of mefenamic acid with a silver nitrate solution in a neutral alcoholic medium. The formed precipitation is quantitatively determined directly or indirectly through the silver content of the precipitation formed or the residual unreacted silver ions in the filtrate by atomic absorption spectrophotometry. The results obtained in both the procedures either in their pure form or in their pharmaceutical formulations are accurate and precise. The stoichiometric relationship of the reaction was studied using lob s continuous variation method, and it was found to be (1 1) drug Ag+ for the mefenamic acid. 

Having established the composition of the complex, the stability constant of the complex was determined by (i) mole ratio method and (ii) continuous variations method. In the former method, the equilibrium considered is... 

In the spectrophotometric method, the molar absorptivity of the complex is an additional variable to be determined. As well, it is necessary to determine the stoichiometry of the complex before calculations can be performed. The mole-ratio and continuous variations methods are useful in determining the stoichiometry. The observation (or lack) of isosbestic points is also a useful guide to the complexity of the system. 

There are different methods to determine the stoichiometry, e.g. Continuous Variation Methods [6], the Slope Ratio Method [7], the Mole Ratio Method [8], and others. Because the Continuous Variation Method is the most popular among these, this method is adopted here to determine the stoichiometry. 

In order to determine the stoichiometry by the Continuous Variation Method, the following four points have to be considered and carried out ... 

The development of a new spectrophotometric method is usually preceded by studies of the colour system (complex composition and stability), which is the basis of the method. Fundamental physicochemical studies of the colour complexes existing in the solution enable one to establish the optimum parameters of the method [74-76]. The composition of the complex (molar ratio of metal to ligand) in the solution is determined by Job s continuous variation method, the Bent and French method of equilibrium shift, the method of mole ratio proposed by Yoe and Jones, and the method based on the ratio of slopes and isosbestic points. Studies of complex compounds in solutions are described in many works, especially [77-80]. 

A). The binding behavior of 43a to Ag" and Pb was studied by a continuous variation method in the extraction experiments (s. Fig. 4a and b). Percent extractions of both cases reached to maximum at 0.5 molar fraction. This fact clearly indicates that both Ag and Pb " form 1 1 complexes with 43a, and also suggests that the Pb and Ag ions fit into the cavity of 43a. The neutralization of the charges between the host and metal cation must occur more favorably with Pb than with Ag, because 1 1 complexes must exist in the organic phase. Accordingly, it is considered that the 43a-Pb complex... 

The binding behavior of 44a and 44b to Ag ions was determined by the continuous variation method (Fig. 4c and d). The maxima are seen at molar fractions larger than 0.5. Moreover, these figure shapes are much different from those of Fig. 4b. Although several kinds of complexes having various host/guest ratios are actually formed, the ratios have not been determined yet. 

Continuous-Variation Method. The molar ratios may also be varied by changing the concentrations of both components while the total number of moles of both com-... 

Several techniques such as the continuous variation method, mote ratio method, solubility phase diagrams, the direct measurement of complex molecular masses, etc. are available for a determination of the stoichiometry of intermolecular complexes. The commonly used mediod is the continuous variation method, which was originally proposed by Ostromislensky in 1911 [17] and modified by Job [18]. 

The stoichiometry of inclusion complexes was estimated by the continuous variation method. The results are shown in Fig. 3. It is clear that the inclusion complexes with 3- and y-CyDs show a 1 1 and 2 1 stoichiometry, respectively. Since the i.c.d. spectrum was unchanged n its general form at the concentration of 2AS ([2AS]) ranging from 10 M to... 

The spectrum of the solution in the visible region was measured with a Hitachi spectrophotometer. Absorptions at 389 nm were measured by a continuous variation method for the solutions of various molar ratios of DEC and EK or polymer matrices to confirm the formation of a charge-transfer complex. 

Figure 6 Continuous variation method (Job Plot) for a hypothetical 1 1 complex formation.

The different methods to determine the stoichiometry of a chemical reaction include continuous variation methods," the slope ratio method, - the mole ratio method, and others. Here we adopt the continuous variation method to determine the stoichiometry since it is the most widely employed method by the community. To determine the stoichiometry of a reaction by the continuous variation method, the following four points must be considered and carried out ... 

Determination of the FLZ.-p-CD Inclusion Complex Stoichiometry by Continuous Variation Method (Job s Plot)... 

Figure 2. Jobs plot (continuous variation method) of FLZ p-CD inclusion complex showing 1 1 stoichiometry.

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