Metal ion solution

However, under anhydrous conditions and in the absence of catalytic impurities such as transition metal ions, solutions can be stored for several days with only a few per cent decomposition. Some reductions occur without bond cleavage as in the formation of alkali metal superoxides and peroxide (p. 84). 

B. Back-titration. Many metals cannot, for various reasons, be titrated directly thus they may precipitate from the solution in the pH range necessary for the titration, or they may form inert complexes, or a suitable metal indicator is not available. In such cases an excess of standard EDTA solution is added, the resulting solution is buffered to the desired pH, and the excess of the EDTA is back-titrated with a standard metal ion solution a solution of zinc chloride or sulphate or of magnesium chloride or sulphate is often used for this purpose. The end point is detected with the aid of the metal indicator which responds to the zinc or magnesium ions introduced in the back-tit ration. 

Plot the titration curve (potential in millivolts vs S.C.E. against volume of standard EDTA solution) and evaluate the end point. In general, results accurate to better than 0.1 per cent are obtained. Brief notes on determinations with various metal ion solutions follow. 

As discussed earlier the whole process is a redox reaction. Selenium is reduced using sodium borohydride to give selenide ions. In the above reaction, the metal ion reacts with the polymer (PVP or PVA) solution to form the polymer-metal ion solution. Addition of the selenide ion solution to the polymer-metal ion solutions resulted in instantaneous change in the colour of the solutions from colourless to orange (PVA) and orange red (PVP). This indicates the formation of CdSe nanoparticles. The addition of the selenide solution to the polymer - metal ion solution resulted in gradual release of selenide ion (Se -) upon hydrolytic decomposition in alkaline media (equation 4). The released selenide ions then react with metal ion to form seed particles (nucleation). 

Cobalt(II)/copper(II) Luminol-H202-cysteine 0.5-10/2-20 2.5/3.0 Metal ion solutions were saturated with oxygen 64... 

Oxide-water interfaces, in silica polymer-metal ion solutions, 22 460—461 Oxidimetric method, 25 145 Oxidization devices, 10 77-96 catalytic oxidization, 10 78—96 thermal oxidation, 20 77-78 Oxidized mercury, 23 181 Oxidized polyacrylonitrile fiber (OPF), 23 384... 

An ion exchanger (0.04 g) and a metal ion solution (10 4 M, 25 ml) were taken into 50 ml Erlenmeyer flasks. Then, the flasks were shaken with a mechanical shaker at 30 °C for 24 h. The metal ion concentration in the aqueous phase was determined by means of ICP-AES. From a decrease of the metal ion concentration in the aqueous phase, uptake of metal ion in mmol/g was calculated. Here, only nitric acid was used in the pH adjustment. 

In direct titration, usually an appropriate buffer solution and a suitable indicator are added to the M2+ (metal-ion) solution and subsequently the resulting solution is titrated with previously standardized disodium-EDTA until the indicator just changes colour. Sometimes, a simultaneous blank determination is also recommended to have a check for the presence of traces of metallic impurities in the reagents. 

In actual practice, an excess of the standard solution of disodium edetate is added to the sample, pH is adequately adjusted for the residual titration with a metal-ion solution e.g., ZnS04 and employing an appropriate indicator which is sensitive enough to the respective titrant. However, the metal ion under estimation remains firmly complexed with the EDTA and offers little interference with the Zn-EDTA complex formed. It has been established experimentally that bismuth readily yields a highly stable complex which may be titrated conveniently between pH 1 and 2. Bismuth forms a stable complex by reacting with EDTA quantitatively at pH 4.0 and, therefore, dithizone is employed as an indicator to detect the end-point for it has a transition state of colour at pH 4.6. 

Table 1 lists some of the metal compounds employed and the results obtained when attempts were made to cast films of the resulting metal ion filled polyimide derived from BTDA + m,m -DABP. Brittle films were produced in most cases regardless of whether the added metal ion was hydrated or anhydrous. The relatively low viscosities of the resulting polyamic acid-metal ion solutions no doubt accounted for this. Addition of AlCl3 6H20 or any simple aluminium salt to the polyamic acid produced immediately a rubbery material that could not be cast into a film. 

The intent of this chapter is not to provide an exhaustive review of chemical- and biosensors and probes, but rather to offer a brief overview of existing optical techniques and an indepth analysis of near-infrared (NIR) fluorogenic probes and sensors for the detection of metal ions, solution pH, and biomolecules and to present some of the latest results. 

Adsorption measurements were made by batch technique at room temperature (25 3°C). Known amounts of tannin resin were placed in 250 mL erlenmeyer flasks containing 100 mL of metal ion solution of known concentration and were stirred for a given time period. The solutions were then filtered, centrifuged and the concentrations of metal ions were measured by AAS. The difference in the metal ion (Pb + and Ztf+) content before and after adsorption represented the amount of Pb and Zn adsorbed by new resin. 

Effect of initial pH on adsorption of Pb + ions were investigated as follows 0.5 g of the resin was weighed and 100 mL of a heavy metal ion solution was added. The pH of each solution was adjusted to desired values. After stirring 5 h the reaction mixture was filtered through membrane filter to remove particulates and analyzed with an AAS. 

Next, place 3 drops of the metal ion solutions on the corresponding areas of the filter paper (indicated by the name of the metal). 

When the irradiation of metal ion solutions is performed in the presence of the ligands CO or PPhs, metal reduction, ligandation, and aggregation reactions compete, leading to reduced metal complexes and then to stable molecular clusters, such as Chini clusters Pt3(CO)6] with m = 3-10 (i.e., 9-30 Pt atoms) [97], or other metal clusters [98]. The synthesis is selective and m is controlled by adjusting the dose m decreases at high doses). The mechanism of the reduction has been determined recently by pulse radiolysis [99]. Molecular clusters [Pt3(CO)6]5 have been observed by STM [100]. 

Although the mechanism of the photo-induced generation of mono- and bimetallic metal clusters, except for the photographic application (Section 20.6), has been studied with considerably less detail than for the radiolytic route, some stable clusters, mostly of noble metals (Ag, Au, Pt, Pd, Rh), have also been prepared by UV excitation of metal ion solutions [129-141]. Generally, halides and pseudo-halides counter anions are known to release, when excited, solvated electrons, which reduce the metal ions up to the zerovalent state. Oxalate excitation yields the strong reducing carbonyl radical COO [30]. Photosensitizers are likewise often added [142]. Metal clusters are photo-induced as well at the surface of photo-excited semiconductors in contact with metal ions [143,144]. 

Figure 13 Scheme of the influence of the dose rate on the competition between the inter-metal electron transfer and the coalescence processes during the radiolytic reduction of mixed metal ion solutions. Sudden irradiation at high dose rates favor alloying, whereas low dose rates favor coreshell segregation of the metals because of metal displacement in the clusters. 

Tubules have also been prepared by swelling thin films of polymerizable diacetylenic phosphatidylhydroxyethanol (choline functionally in 21 is replaced by hydroxyethanol) in aqueous metal ion solutions above the phase transition temperature of the lipid. Various cylindrical structures were observed upon swelling the lipid in the presence of mono- and divalent cations. In contrast, no definable microstructures were noted in the absence of cations [362],... 

Transition from non-metallic clusters consisting of only a few atoms to nanosized metallic particles consisting of thousands of atoms and the concomitant conversion from covalent bond to continuous band structures have been the subject of intense scrutiny in both the gas phase and the solid state during the last decade [503-505]. It is only recently that modern-day colloid chemists have launched investigations into the kinetics and mechanisms of duster formation and cluster aggregation in aqueous solutions. Steady-state and pulse-radiolytic techniques have been used primarily to examine the evolution of nanosized metallic particles in metal-ion solutions [506-508]. 

The upshot is that the Born theory of solvation fails because it regards the solvent as a continuous dielectric, whereas in fact solute ions (especially metal cations with z > 1) often interact in a specific manner with solvent molecules. In any event the molecular dielectric is obviously very lumpy on the scale of the ions themselves. The Born theory and other continuous dielectric models work reasonably well when metal ion solute species are treated as solvent complexes such as Cr(OH2)63+ rather than naked ions such as Cr3+, but the emerging approach to solvation phenomena is to simulate solvation dynamically at the molecular level using computer methods. 

Dropwise addition of stoichiometric H2O or transition metal ion solution... 

Reference-metal-ion solution Salt solution Liquid interface (with fluid) or porous plug... 

Chelating resins are iminodiacetate type, polyamine type, or glucamine type. They exhibit high retention of some metals, such as heavy metals from alkali metal ion solutions. 

Prepare 0.100 M stock metal-ion solution in Milli-Q water in a 1 L volumetric flask. Prepare dilute metal-ion solutions by serial dilution of the stock metal-ion solution in 50 mM ammonium acetate buffer (pH 7.0). 

Metal Ion Solution Conditions Electrolysis Conditions Interferences... 

Metal Ion-Solute. Transition metals have been loaded onto classical LC columns and used for selective separations (21). More recently successful attempts have been made to control selectivity by metal additions directly to the mobile phase (22). This is a form of ion pairing, but the pairing agent is polar instead of hydrophobic. Silver ion has been used for the separation of olefins (23). M. deRuyter and A. deLeenheer have employed argentation chromatography to resolve difficult mixtures of Retinyl esters (24). 

Chelated Metal Ion-Solute. If the metal is first chelated with a relatively hydrophobic chelating agent, solute interactions will increase retention. Cooke et al C25) have developed such a technique using 4-dode-cyldiethylenetriamine and Zn(ll). Not only does this chelated metal greatly increase retention for certain anionic solutes, presumably by an ion pairing interaction, but the relatively rigid conformation of the metal chelate imparts marked selectivities. 

Cobalt recovery from acidic metal ion solutions is impeded by the evolution of hydrogen. However, if the pH of the solution is gradually increased, it is found that at pH > 4 this deposition is possible. 

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