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Metal ions methods

The preparation methods of the colloidal dispersions of bimetallic nanoclusters are summarized in Fig. 3.19. Method no.l is the coreduction of the bimetallic complex which is produced by the complexation of two kinds of metal ions. Method no.2 is the coreduction of two kinds of metal ions in solution. It is sometimes rather difficult to distinguish method no. 1 from method no. 2. Method no. 3 shows a successive reduction method in which the second metal ions can be added to the dispersions after the first metal ions are reduced to form nanoclusters. No. 4 is a new method in which the dispersions of two kinds of metal nanoclusters are mixed in solution to form the dispersion of bimetallic nanoclusters. [Pg.186]

High-precision and high-accuracy determination of amino acids is difficult. Let us examine the possibilities of an indirect approach through dissolving a metal ion compound followed by the highly accurate EDTA (or other) metal ion methods. An iodide-Cu(II) method was proposed in 1950. Likely candidates are Cu(II) and Hg(II), which form very stable complexes with amino acids. The glycinate complexes have the stability constants shown in Table 11-3. The objective is to get quantitative dissolving of a low solubility metal ion compound when excess of it is stirred with a measured... [Pg.202]

Keywords cadmium calcium equilibrium constants magnesium metal ions methods ribozymes RNA zinc... [Pg.193]

Finally, micellar systems are useful in separation methods. Micelles may bind heavy-metal ions, or, through solubilization, organic impurities. Ultrafiltration, chromatography, or solvent extraction may then be used to separate out such contaminants [220-222]. [Pg.484]

METHODS FOR REMOVING THE METAL IONS RESPONSIBLE FOR HARDNESS IN WATER... [Pg.274]

Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. [Pg.165]

The equilibrium constants obtained using the metal-ion induced shift in the UV-vis absorption spectrum are in excellent agreement with the results of the Lineweaver-Burke analysis of the rate constants at different catalyst concentrations. For the copper(II)ion catalysed reaction of 2.4a with 2.5 the latter method gives a value for of 432 versus 425 using the spectroscopic method. [Pg.58]

In the presence of many metal ions, diorthohydroxyazo dyes exhibit two polarographic reduction waves, the first due to free dye and the second to metal-dye complex. Highly sensitive analytical methods based on this principle have been developed for example, Ni or Fe may be determined in the presence of an excess of aluminum thank to thiazolylazo derivatives (563). [Pg.153]

Description of the Method. The operational definition of water hardness is the total concentration of cations in a sample capable of forming insoluble complexes with soap. Although most divalent and trivalent metal ions contribute to hardness, the most important are Ca + and Mg +. Hardness is determined by titrating with EDTA at a buffered pH of 10. Eriochrome Black T or calmagite is used as a visual indicator. Hardness is reported in parts per million CaCOs. [Pg.326]

EDTA forms colored complexes with a variety of metal ions that may serve as the basis for a quantitative spectrophotometric method of analysis. The molar absorptivities of the EDTA complexes of Cu +, Co +, and Ni + at three wavelengths are summarized in the following table (all values of e are in cm )... [Pg.451]

Noncnzymc-Catalyzcd Reactions The variable-time method has also been used to determine the concentration of nonenzymatic catalysts. Because a trace amount of catalyst can substantially enhance a reaction s rate, a kinetic determination of a catalyst s concentration is capable of providing an excellent detection limit. One of the most commonly used reactions is the reduction of H2O2 by reducing agents, such as thiosulfate, iodide, and hydroquinone. These reactions are catalyzed by trace levels of selected metal ions. Eor example the reduction of H2O2 by U... [Pg.637]

Inorganic flocculants are analyzed by the usual methods for compounds of this type. Residual metal ions in the effluent are measured by spectroscopic techniques such as atomic absorption. Polymeric aluminum species formed in solution have been characterized by Al-nmr (64). [Pg.36]

At high neutralization levels with alkaH metal ions, many ionomers spontaneously form coUoidal suspensions in water when stirred vigorously at 100—150°C under pressure. Depending on soHds content and acid level, the dispersions range in viscosity from water-like to paste-like. These provide convenient methods for applying thin coatings of ionomers to paper and other substrates. [Pg.407]

The principle of this method depends on the formation of a reversible diastereomeric complex between amino acid enantiomers and chiral addends, by coordination to metal, hydrogen bonding, or ion—ion mutual action, in the presence of metal ion if necessary. L-Proline (60), T.-phenylalanine (61),... [Pg.279]

Another method employed is the treatment of aqueous solutions of aminophenols with activated carbon (81,82). During this procedure, sodium sulfite, sodium dithionite, or disodium ethylenediaminotetraacetate (82) is added to increase the quaUty and stabiUty of the products and to chelate heavy-metal ions that would catalyze oxidation. Addition of sodium dithionite, hydrazine (82), or sodium hydrosulfite (83) also is recommended during precipitation or crystallization of aminophenols. [Pg.311]

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. [Pg.245]

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). [Pg.17]

Chelation itself is sometimes useful in directing the course of synthesis. This is called the template effect (37). The presence of a suitable metal ion facihtates the preparation of the crown ethers, porphyrins, and similar heteroatom macrocycHc compounds. Coordination of the heteroatoms about the metal orients the end groups of the reactants for ring closure. The product is the chelate from which the metal may be removed by a suitable method. In other catalytic effects, reactive centers may be brought into close proximity, charge or bond strain effects may be created, or electron transfers may be made possible. [Pg.393]

There are a number of ways to obtain color in a ceramic material (1). First, certain transition-metal ions can be melted into a glass or dispersed in a ceramic body when it is made. Although suitable for bulk ceramics, this method is rarely used in coatings because adequate tinting strength and purity of color caimot be obtained this way. [Pg.425]

Surface preparation of the dental implant prior to implantation wiH have an effect on corrosion behavior, initial metal ion release, and interface tissue response (316). The titanium and titanium aHoy dental implants in present use have many forms to assist bone ingrowth attachment including cylinders with holes, screw threaded surfaces, porous surfaces, and other types of roughened surfaces. Methods used to produce porous surfaces iaclude arc plasma... [Pg.495]

Most of ions do not interfere to the determination of P(V) or As(V). Big access of colored transition metals can be tolerated by using those metals solution as reference solution. It was already shown that high selectivity of the proposed method with respect to metal ions gave the opportunity to determine phosphoms in a number of nonferrous (brass, bronze) and ferrous alloys without preliminai y sepai ation. [Pg.87]


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See also in sourсe #XX -- [ Pg.365 ]




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