Determination of Stoichiometry

The following sections deal with the principle and also the practical issues necessary for an understanding and performance of the above four points in this order. 

A Practical Course of Binding Constant Determination by UV/vis Spectroscopy 

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 Eq. (2.14) is then differentiated, and the is substituted by zero. Then the x-coordinate at the maximum in the curve is obtained. 

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Mountain BW, Seward TM (1999) The hydrosulphide/sulphide complexes of copper(I) experimental determination of stoichiometry and stability at 22°C and reassessment of high temperature data. Geochim Cosmochim Acta 63 11-29... 

Ackers, G. K., and T. E. Thompson Determination of stoichiometry and equilibrium constants for reversible associating systems by molecular sieve chromatography. Proc. Natl. Acad. Sci. 53, 342 349 (1965). 

The effects of an absorption edge are shown in an important case for semiconductors in Figure 4.4. This shows the real and imaginary parts of the scattering factors for gallium and arsenic near the K absorption edges. The exchanges in values, and resultant intensities, that are shown can and have been used for composition- sensitive experiments such as the determination of stoichiometry in III-V semiconductors. However, the tunabihty of a synchrotron radiation source is required for such experiments in most cases. 

The electrochemical properties of Cd(II) complexes with inorganic ligand presented in early papers were discussed by Hampson and Latham [72]. Later, electrochemical investigations of cadmium complexes were oriented on the mechanism of complex formation, determination of stoichiometry and stability constants, mechanisms of reduction on the electrodes, and evaluation of kinetic parameters of these processes. The influence of ligands and solvents on stability and kinetic parameters of electroreduction was also studied. 

Chemical characterization of solids generally involves the characterization of the major phase, which includes the determination of stoichiometry, homogeneity and... 

Table 9.15 Comparison of determinations of stoichiometry in thin Ba0,7Sr0 3Ti-, 03 perovskite layer measured by ICP-MS using different instruments and XRF.

At present, advanced mass spectrometric techniques have been successfully established among a multitude of quite different analytical methods as very powerful tools which are increasingly being employed for high tech research topics and for daily routine analyses in many laboratories worldwide. Numerous different applications in various fields of use, as demonstrated in the several chapters of this book, illustrate the excellent current capability of inorganic mass spectrometry in the multi-element determination of elements in a wide dynamic range (from % range for determination of stoichiometries, e.g., in layered materials, down to the extreme ultratrace level, e.g., in environmental research, speciation analysis and isotope ratio measurements). 

S. Scaccia and M. Carewska, Determination of Stoichiometry of Li, +)Co02 Materials by Flame Atomic Absorption Spectrometry and Automated Potentiometric Titration, Anal. Chim. Acta 2002,453, 35. 

Figure 8. Time dependence of short-circuit current for several Cd(Se,Te) electrodes in 2 M KOH, S and S. Further details as in Figure 2. See Table I for determination of stoichiometry (upper numbers, Se/Te) and crystal structure flower numbers) (1).

A Shimadzu UV-265FW spectrophotometer was used for the determination of stoichiometry of the reactions. Kinetic measurements were carried out with excess amount of reducing reagents by using a Unisoku RA-401 stopped-flow apparatus. Electrochemical measurements were carried out by a BAS-IOOB Electrochemical Analyser. 

In the following subsections experiments are described which indicate that CO2 reduction to methylene-H4MPT is driven by a primary electrochemical Na potential generated by formaldehyde reduction to CH4. These experiments include (1) studies of the mode of energy transduction of the reverse reaction, the exergonic formaldehyde oxidation to CO2 and 2H2 (2) experiments on the effects of ionophores and inhibitors on CH4 formation from CO2/H2 and CH4 formation from formaldehyde/H2, and the determination of stoichiometries of primary Na" translocation. 

Stoichiometries of primary Na translocation. Further support for the conclusion that CO2 activation is driven by A/iNa" came from the determination of stoichiometries of primary Na transport coupled to CH4 formation from CO2/H2 and from formaldehyde/H2. Na" transport experiments were performed with whole cells of Methanosarcina barkeri equilibrated with Na the stoichiometry of Na export was... 

Table niA. Determination of stoichiometry of sKit/SCF complex with an extinction coefficient [0.S8S ml/(mg Cm)] calculated from the method described in this paper... 

Fig. 2.2. Determination of stoichiometry from the x-coordinate at the maximum of the curve in Job s Plot.

Electrospray ionization mass spectrometry (ESI-MS) has a well-known ability to handle non-covalent assemblies [29]. The determination of stoichiometry, identification of binding parmers and site specificity, analysis of protein folding, and determination of affinity constants are aU examples of characterization of supramolecular assemblies by mass spectrometry [30-32],... 

Type I - viscosity isotherms are monotonically convex in direction to the composition axis (dr / 3x 0,3 r / dx >0). Chemical interaction influences the shape of viscosity isotherm that is typical when experimental isotherm is situated above the curve calculated under assumption of absence of any interaction (i.e., from equation [9.31a]). The means of increasing heteromolecular association and determination of stoichiometry of associates for this type of isotherms was discussed elsewhere. Piperidine-aniline system is an example of this kind of interacting system. 

Determination of stoichiometry of interaction between the components of the mixed solvent is discussed elsewhere. ... 

Photosystem I (PS I) reaction center complex consists of two large subunits which carry antenna chlorophyll P-700 and early electron acceptors and several small subunits, one of which contains the iron-sulfur centers, F and Fg. Because the PS I complexes are usually isolated with detergents, careful evaluation of detergent-effects, such as solubilization of chlorophyll a, or inactivation of P-700, is essential for determination of stoichiometry of subunit polypeptides and functional constituents in the complex. Recently, we have shown that the differential extinction coefficient of P-700 is markedly affected by sodium dodecyl sulfate (SDS) which induces a band-shift of chlorophyll molecules at 690 nm [1]. Herein, we report effects of other detergents on the extinction coefficient of P-700 and provide a simple method to estimate the extinction coefficient in PS I preparations treated with various detergents. Using the extinction values thus determined,... 

El-Kemary, M.A. El-Mehasseb, I.M. Global and distribution analysis of fluorescence decays and spectrofluorimetric determination of stoichiometry and association constant of... 

Determination of Stoichiometries by EQCM Technique (Values, y) for Metal Phases [Metal2 , M+, (MX)y] Obtained with Platinum and Palladium in Super-Dry DMDF in the Presence of Alkaline Iodides... 

Turning now to chemical and compositional information an approach similar to that de.scribed above can be taken in order to determine chemical states (e.g., oxidation state, bonding, compound or species identification) and composition (c.g., quantification, for determination of stoichiometry, and for impurity identification). 

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