Diethyldithiocarbamate metal complexes

Multi-element analyses involving solvent extraction and high performance liquid chromatography (HPLC) have also been described. The extracts, containing metal-chelate complexes with sulphur-containing reagents, such as dithizone and diethyldithiocarbamate, were used directly for determination of the metals by HPLC.14... 

A number of metal ions may be separated by TLC as their diethyldithiocarbamate (DDTC) chelates and are detected by a ligand-exchange reaction between a metal-calcein complex and the DDTC chelate [198]. The limits of visual detection are 0.1-2 ng per spot for the metal ions. 

Spectrophotometric methods using Na-DDTC are rather insensitive since the colours of metal complexes with DDTC are not intense. Complexes with Cu, Bi, and Mn are among the most intensely coloured diethyl dithiocarbamates. The yellowish Ag-DDTC is used in the determination of arsenic (reaction with ASH3, see Section 8.2.2). Fig. 19.1 shows the absorption spectra of some metal diethyldithiocarbamates. 

The stability of diethyldithiocarbamate complexes with metals decreases in the following order ... 

Quantitative. Classically, silver concentration in solution has been determined by titration with a standard solution of thiocyanate. Ferric ion is the indicator. The deep red ferric thiocyanate color appears only when the silver is completely titrated. Gravimettically, silver is determined by precipitation with chloride, sulfide, or 1,2,3-benzotriazole. Silver can be precipitated as the metal by electrodeposition or chemical reducing agents. A colored silver diethyldithiocarbamate complex, extractable by organic solvents, is used for the spectrophotometric determination of silver complexes. 

Nalbandyan, 1982 Hodgson and Fridovich, 1975 Asada et al., 1975), whereas azide inhibits the enzymes in the following order iron > manganese > copper/zinc superoxide dismutase (Misra and Fridovich, 1978). Diethyldithiocarbamate is another well-characterized inhibitor of the copper/zinc superoxide dismutase (Heikkila et al., 1977). It forms a complex with the copper and removes the metal from all the protein ligands. The copper-diethyldithiocarbamate complex can be separated without affecting the zinc content of the protein (Cocco et al., 1981). 

Diethvldithiocarbamato Mercury (II). The incorporation of metal-ligand complexes within polymeric membranes for the development of new anion sensors is not limited to the use of metalloporphyrins. Indeed, recent studies with the Hg (II) complex of diethyldithiocarbamate (Hg(DDC)2) have yielded a new membrane electrode with relatively high... 

Column chromatographic systems can also be used to separate trace metals by complexation methods. Knapp et al. (325) used diethyldithiocarbamate solution on a Chromosorb W-DMCS column to concentrate metals and either eluted them in bulk for x-ray analysis or sequentially for atomic absorption analysis. Acetylacetonates have also been used for column separations (326). 

Wang and co-workers have recently reported a generalized strategy for the synthesis of a variety of ternary metal sulfides with controlled size, morphology, (Fig. 25) crystallographic phase and stoichiometric composition. This one pot synthetic approach is primarily based on co-thermal decomposition of diethyldithiocarbamate complexes of corresponding metals in oleylamine and dodecanethiol surfactants. 

Mobile phase Af, toluene-chloroform (SO l) Mi = benzene-methyl isopiopylketone (SO I) Mi = raethanol-water-acetic acid (SO 30 4). Conditions Ascending technique, run IS cm, layer thickness 0.2S ram, activation at I20°C for 30 min. Detection (a) metal dithizonates were self detected, (b) S% aqueous copper sulfate solution for metal diethyldithiocarbamates and (c) 0.2S% PAN [I-(2-pyridylazo)-2-naphthoI solution] in methanol followed by exposure to ammonia vapors for metal ions. Remarks (1) Best separations on RP-18 with M (2) The extracts of complexes of metals originating from biological samples require careful protection from environmental contamination and (3) The developed TLC method was applied for analysing human placentas collected from patients of the obstetrics Clinic in Tychi (Poland) for Pb, Cd, Zn, Cu, Ni, Mn, and Co content. 

Currently, the Cambridge Structural Database contains data for 1500 chelating dithiocarbamate ligands. Table III provides structural data for simple diethyldithiocarbamate complexes of aU the transition metals (where available). 

Before considering the special requirements for automated on-line determination of metals from industrial effluents, it is worthwhile examining the features of standard laboratory procedures associated with the off-line determination of copper as a dithiocarbamate complex by liquid chromatography with electrochemical detection. The off-line determination of copper as its diethyldithiocarbamate complex in aqueous samples, zinc plant electrol3d e, and urine have been described [3, 7, 10] using reverse phase liquid chromatography with amperometric detection. A standard instrumental configuration for the conventional laboratory off-line method as used in these studies is depicted in Fig. 7.2. 

The mechanism proposed72 involves initial nucleophilic attack at the carbene carbon by the dithiocarbamate anion, effectively resulting in addition across the metal-carbon bond. Rearrangements of the dithiocarbamate ligands then form an V-allyldithiocarbamate species Complex 53 was isolated from the reaction mixture of 51 with the diethyldithiocarbamate and identified by X-ray crystallography. 

The most versatile reagent of this group is diethyldithiocarbamic acid (40), which forms coloured and extractable complexes with very many metals, selectivity being assured by control of the pH and the presence of masking agents.52 Here again the practical disadvantages stem from the ease of oxidation and many alternate carbamic acids derived from pyrrolidine and other dialkylamines have been studied. 

Edward Iratami [273] applied high performance liquid chromatography to the determination in river water of mercury(II), copper(II), nickel(II), cobalt(II) and lead(II) as their dithizonates and their diethyldithiocarbamates. The metals were first complexed, then the complexes... 

Two crystalline modifications of mercury(n) NN-diethyldithiocarbamate have been reported.208 The a-form consists of dimeric Hg2(S2CNEt2)4 units, in which the metal atom is five-co-ordinate, in a manner similar to analogous zinc and cadmium complexes. The P-form is composed of essentially monomeric Hg(S2CNEt2)2 units, with the two ligand molecules co-ordinated in a plane through the S atoms (Hg—S = 2.40 A). 

Interferences Metals or salts of metals such as chromium, cobalt, copper, mercury, molybdenum, nickel, palladium, and silver may interfere with the evolution of arsine. Antimony, which forms stibine, is the only metal likely to produce a positive interference in the color development with the silver diethyldithiocarbamate. Stibine forms a red color with silver diethyldithiocarbamate that has a maximum absorbance at 510 nm, but at 535 to 540 nm, the absorbance of the antimony complex is so diminished that the results of the determination would not be altered significantly. 

The most widely applied reagents have been chelating agents which will complex with many metals, e.g. dithizone and the various thiocarbamate derivatives such as diethyldithiocarbamate and pyrrolidine dithiocarbamate. The latter agent as the ammonium salt (APDC) has been shown to complex some thirty elements [19] most of which can be readily extracted into various solvents. 4-Methylpentane-2-one (methyl isobutyl ketone or MIBK) is usually the favoured solvent because of its excellent compatibility with flames. The solubility of MIBK in water is not negligible and this limits the available concentration factor to ten higher molecular weight ketones (e.g. decan-2-one) offer better concentration factors and chloroform up to fifty times, but this latter solvent is only really suitable for electrothermal atomisation. 

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