Transition metals spectrophotometric determination

A determination of dimethyl sulphoxide by Dizdar and Idjakovic" is based on the fact that it can cause changes in the visible absorption spectra of some metal compounds, especially transition metals, in aqueous solution. In these solutions water and sulphoxide evidently compete for places in the coordination sphere of the metal ions. The authors found the effect to be largest with ammonium ferric sulphate, (NH4)2S04 Fe2(S04)3T2H20, in dilute acid and related the observed increase in absorption at 410 nm with the concentration of dimethyl sulphoxide. Neither sulphide nor sulphone interfered. Toma and coworkers described a method, which may bear a relation to this group displacement in a sphere of coordination. They reacted sulphoxides (also cyanides and carbon monoxide) with excess sodium aquapentacyanoferrate" (the corresponding amminopentacyanoferrate complex was used) with which a 1 1 complex is formed. In the sulphoxide determination they then titrated spectrophotometrically with methylpyrazinium iodide, the cation of which reacts with the unused ferrate" complex to give a deep blue ion combination product (absorption maximum at 658 nm). 

The advantage of the kinetic approach to determining acidity and other equilibrium constants lies in the fact that species that do not react with the added substrate do not interfere with the determination. This is in contrast to spectrophotometric titrations, where the change in absorbance with changing pH may be caused by species unrelated to the equilibrium of interest. Such situations are quite common in studies of unstable species encountered in activation of small molecules by transition metal complexes where several species with ionizable hydrogen atoms may coexist in solution. 

Preparation of Con A Derivatives. Ca -Zn -Con A was obtained from Miles-Yeda. Ca +-Mn -Con A was prepared as previously described (6). Atomic absorption analysis of these two Con A preparations showed essentially equal amounts of the transition metal ion and calcium ions. Sample solutions (0.6 ml) contained Con A at the appropriate concentration in pH 5.60, 0.1N potassium acetate buffer, y = 1.0 in potassium chloride. The final protein concentration was determined spectrophotometrically using = 12.4 at 280 nm ( 7,j)). 

The link between specific transition metals and various disease processes has prompted research interest into new and more effective bioanalytical methods to determine transition metals in physiological fluids. Traditionally clinical chemistry laboratories have used atomic absorption spectrophotometric (AAS) techniques to determine transition metals in physiological fluids. Although both low and high serum levels of various transition metals such as copper, iron and also zinc have been associated with various disease processes, the exact mechanisms underlying many of these conditions are still not completely understood. The following subsections describe some of the most prominent and best understood conditions associated with increased or decreased blood plasma levels of transition metals. 

A number of inorganic species also absorb. We have noted that many ions of the transition metals are colored in solution and can thus be determined by spectrophotometric measurement. In addition, a number of other species show characteristic absorption peaks, including nitrite, nitrate, and chromate ions, the oxides of nitrogen, the elemental halogens, and ozone. 

Pacey s group [28] reported an extremely selective spectrophotometric method for the determination of chlorine dioxide which exhibited 5400-fold higher selectivity for chlorine dioxide over chlorine. The high selectivity resulted from a syneigistic combination of the removal of transition metal interferents by gas-diffusion kinetic discrimination in gas transfer efficiency across the membrane and optimization of the acceptor stream composition by the addition of oxalic acid. 

Chattopadhyay et al [Ch 76a, Ch 76b, Ch 77] used a spectrophotometric stopped flow technique to study the kinetics of formation and dissociation of a large number of nickel complexes, with a metal to ligand ratio of 1 1, in various non-aqueous solvents. When their findings were compared with the results obtained earlier in investigations of analogous complexes of other transition metal ions [Ch 73, Ch 74], it was established that in most of the systems the above reaction follows an /d mechanism. The step determining the reaction rate was found to be the exchange between the solvent bound in the coordination sphere of the metal and the... 

Metal cation recognition probes Some metals, notably the transition metals, readily form complexes with organic molecules, resulting in changes to optical properties, most commonly absorbance. This phenomenon is commonly exploited in standard methods for the spectrophotometric determination of metal cation concentrations [8] and standard test kits for a variety of metals are commercially available [12]. More complex probes based on a cation binding site linked to a fluorophore or chromophore reporter have also been developed [13]. The cation... 

HCI-n-butanol-acetone (3 1 6) W2S = HCl-n-pentanol-acetone (3 1 6) W27 = HCl-n-hexanol-acetone(3 1 6) M28-M.M = HCl-DMSO-piopanol-2 in 1 1 1, 2 1 1, 1 2 1, and 1 1 2 ratio respectively. Detection Conventional spot test reagents used for detection of Cu, Ni, Coi, 2j, Mn, and Fe . Conditions Ascending technique, run 10 cm. layer thickness 0.25 mm. plate activation at 110 2°C for I h. loading volume 10 Remarks Qualitative separation of transition metal chlorosulphates and quantitative spectrophotometric determination of cobalt chlorosulphate were discussed. Source A. Mohammad, K. T. Nasim, J. Ahmad, and M. Najar P. A.. Analusis. 23 243 (1995). 

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