Metal dithizones techniques

Diphenylthiocarbazone ( dithizone ) forms intensely colored complexes with, for example, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Cd, Pt, Au, and Hg, which are soluble in CCLi and CHCI3, a property which facilitates then-separation and individual determination.Solutions ofmost metal dithizonates in organic solvents have the interesting property of being photochromic (see Photochromism), and the relatively long half-life of the photoexcited mercury(II) dithizonate complexes (ti/2 ca. 1 min) has facilitated then-investigation by conventional specttoscopic techniques. ... 

In addition to distribution chromatographic of ions on paper by utilization of various spray reagents to help detection, thin-layer chromatography of metal chromatography of metal chelates, more than any other technique, has been widely applied with metal dithizonates in particular ... 

Mobile phase M, = toluene-chloroform (50 1) A/j = benzene-methyl isopropylketone (50 1) Mi = methanol-water-acetic acid (50 30 4). Conditions Ascending technique, run 15 cm. layer thickness 0.25 mm, activation at 120°C for 30 min. Detection (a) metal dithizonates were self detected, (b) 5% aqueous copper sulfate solution for metal diethyidithiocarbamates and (c) 0.25% PAN [l-(2-pyridylazo)-2-naphthol solution) in methanol followed by exposure to ammonia vapors for metal ions. Remarks (1) Best separations on RP-18 with My (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. 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

Mercury and its compounds may also be determined by ICP/AES. The method, however, is less sensitive than the cold vapor-AA technique. The metal also can be measured at low ppb level by colorimetry. Mercury ions react with dithizone in chloroform to show an orange color. Absorbance is measured at 492 nm using a spectrophotometer. 

When samples are dry ashed for Sn determination, it is theoretically possible to volatilize the metal during the process, just as for Cd and Pb. This does not seem to be the case in practical work, though. Results from dry ashing have compared very well with results obtained with other techniques, such as HC1 extraction or the dithizone method. It is crucial, however, that the ashes are dissolved in HC1 and not HNO3. 

The use of imprinted polymer ion separation and photometric detection has been demonstrated for Pb [19] and for U02 [35]. In the case of Pb ", the imprinted Pb " resin described above was packed into columns and used to remove Pb " from tap and seawater at a variety of pH values [8], The extraction efficiency of the imprinted resin was compared to the efficiency of an imidodiacetate resin (Chelex-100), a thiol-functionalised resin (Duolite G-73) and a high-capacity polyacrylic acid/polyvinyl alcohol resin (a proprietary NASA resin). The imprinted polymer s extraction efficiency was equal or better than the other resins and the effluents from the imprinted polymer resin were shown to be virtually free of contamination by other metal ions (Fig. 19.13). The purity of the effluent allowed the determination of Pb using a very non-specific colorimetric reagent, dithizone. The method is suitable for automation as an FIA technique. 

A dithizone/chloroform extraction technique for separating ng/l-levels of nickel (Cd, Cu, Zn) from sea water has been developed. The nickel extraction requires an addition of dimethylglyoxime. The metals are concentrated from 100 ml of sea water into 2.0 ml of dilute nitric acid 80). 

The selectivity of spectrophotometric methods has been greatly increased by the development of derivative spectrophotometry (see Chapter 1.5). Derivative spectrophotometry enables one to single out, by means of various mathematical algorithms of data processing, a separate signal due to a selected component, from the sum of absorbances of the analysed mixture. This technique was successfully applied in determinations of a number of elements in mixtures such as Pd, Pt and Au [37], Pd and Pt in iodide solutions [38], Au, Pd and Pt in bromide solutions [39], Ru(IIl) and Rh(IIl) in the form of octadecyldithiocarbamate complexes [40], Ru and Os in chloride solutions [41], Cu, Hg and Pb as dithizonates [42], complexes of various metals with 4-(2-pyridylazo)resorcinol [43], Fe(IIl) with EDTA in the presence of Cr(III), A1 and Mn [44], Cr(III) and Cu(II) with EDTA [45], and Cu and Co in a flow system [46]. Derivative spectrophotometry was also used in the study of Sr- complexing reactions with various crown ethers [47]. 

Chelating resin formed by immobilization of sulfonated dithizone on the anion exchanger Tkmberlite IRA-400 was applied in concentration of heavy metal ions, i.e. Pd(II), Ni(II), Co(II), Cu(II) and Pb(II) in the water samples collected in Japan. The first four elements were determined by the GFAAS technique but Pb(II) by HGAAS. The affinity series of the studied ions towards the present resin is as follows Pd(II) > Cu(II) > Co(II) > Pb(II) > Ni(II) [52]. 

Selective solid-phase extractors and preconcentrators of Hg(II) were synthesized and studied. These modified silica gel phases are based on chemical immobilization and physical adsorption of dithizone as well as chemical immobilization of dithiocarbamate on some amine-modified silica gel phases. The mmoFg values as the metal capacities of these modified silica gel phases were determined for a series of metal ions under the effect of pH of metal ions and the equilibration shaking times by the batch equilibrium technique. The modified silica gel phases were found to exhibit excellent affinity toward selective extraction of Hg(ll) in presence of other interfering metal ions. The potential applications of these modified silica gel phases as selective solid-phase extractors and preconcentrators for Hg(II) from natural water samples were also studied and the results indicated excellent extraction of Hg(II) with insignificant contributions by matrix effects. " " ... 

Stationary phase (a) aminoplast (carbamide-formaldehyde polymer), (b) Cellulose MN 300. Mobile phase S = water S2 = ethanol-water (2 3) S3 = ethanol-2-propanol-S M HCl (2 2 2) S< = ethanol-2-propanol-5 M HCI (2 1 2) S, = acetone-S M HCI (2 1) S = 2-butanol-acetone-5 M HCI (2 1 2) S-, = l-butanol-S M HCI (2 1). Detection (a) saturated aqueous solution of (NH4)2S. (b) 0.1% solution of dithizon in chloroform and (c) 0.5% solution of 8-hydroxyquinoline in water-ethanol (40 60). After spraying the chromatograms were exposed to ammonia and the spots were visualized under UV light at 254 nm. Conditions Ascending technique glass plates (20 x 20 cm) coated with slurried aminoplast powder in water (2g aminoplast/plate) were air-dried at room temperature. Remarks Metal ions with different valency states are resolved clearly on aminoplast layers (Fig. 9). The total molecular structure of polymer controls the retention mechanism of metal ions. Source N. U. Perific, S. M. Petrovid, and S. Podunavac, Chromatographia, 31 281 (1991). 

Conditions Ascending technique, layer thickness 0.25 mm. run 10 cm. plate activation for I h at I00°C. Detection 1% Aqueous potassium ferrocyanide solution for Cu and Fe chlorosulfates 1% alcoholic dimethylglyoxime for Ni and Co chlorosulfates 0.5% dithizone in chloroform for Zn and Mn chlorosulfates. Remarks Double spots in most cases and triple spots in few cases were observed. Qualitative separation of transition metals as their chlorosulfates is possible. Source A. Mohammad and J. Ahmad, J. Planar Chromatogr., (communicated). 

O.OS, 0.1,0.15 and 0.2 M aqueous solutions of sodium malate respectively. Mf-Mg are 0.05, 0.1, 0.15, and 0.2 M aqueous solutions of sodium malonate respectively. The pH value of all mobile phases was kept at 4. Detection 1% Alcoholic solution of dimethylglyoxime (Ni " "), 0.02% dithizone in carbon tetrachloride (Pb, Zn ), 2% aqueous potassium ferrocyanide (Fe , Cu ) and 0.1% aqueous 4-(2-pyridylazo) resorcinol (Mn ) solutions were used as detection reagents. Conditions Ascending technique, mobile phase pH was adjusted by adding HCI or NaOH, loading volume 2-3 ml, development time 15 min. Remarks Examination of variation in R/values of metal ions with respect to concentration and pH of mobile phase additives. The detection and separation of metal ions in wastewater samples (composition Fe-Cu-Zn) of decarbonization plant was performed on silica layer using 0.1 M sodium malate solution (pH 4) as mobile phase. By present method, metals Fe (0.2- 0.56 mg/L, HRf = 77), Cu (0.1-0.57 mg/L, HRf = 93) and Zn (0.03-1.6 mgA., hR, = 69) were detected in different samples of wastewater of decarbonization plant. 

Reverse Displacement, In cases where elements of low extractability are to be separated (and, therefore, direct selective extraction is impossible because of the presence of easily extractable elements) reverse displacement can be used to separate the element of interest. The method is also applicable when, because of the low stability constant of the complex, substoicheiometric extraction is impossible. The technique involves total extraction of the element, removal of excess reagent if necessary, and displacement of the element back into an aqueous phase by reaction of the organic extract with a substoicheiometric amount of a suitable, more extractable, metal ion. For example, the method of Adamek and Obrusnik involves a preliminary total extraction of T1 as dithizonate and a substoicheiometric displacement of T1 by Hg + into the aqueous phase. The method was applied to the activation analysis of Tl, using the 4.3 min isotope, in the concentration range 1—100 p.p.m. Obrusnik has also reported the use of a similar separation method for the activation analysis of In under the equivalent title of replacement substoicheiometry. This method can be used for the determination of In by the (n,y) reaction and of Sn by the Sn(n,y) ) "In reaction. 

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