Dithizone extractions

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

In many applications, such as the analysis of mercury in open ocean seawater, where the mercury concentrations can be as small as 10 ng/1 [468,472-476], a preconcentration stage is generally necessary. A preliminary concentration step may separate mercury from interfering substances, and the lowered detection limits attained are most desirable when sample quantity is limited. Concentration of mercury prior to measurement has been commonly achieved either by amalgamation on a noble-metal metal [460,467, 469,472], or by dithizone extraction [462,472,475] or extraction with sodium diethyldithiocarbamate [475]. Preconcentration and separation of mercury has also been accomplished using a cold trap at the temperature of liquid nitrogen. 

Armannsson [659] has described a procedure involving dithizone extraction and flame atomic absorption spectrometry for the determination of cadmium, zinc, lead, copper, nickel, cobalt, and silver in seawater. In this procedure 500 ml of seawater taken in a plastic container is exposed to a 1000 W mercury arc lamp for 5-15 h to break down metal organic complexes. The solution is adjusted to pH 8, and 10 ml of 0.2% dithizone in chloroform added. The 10 ml of chloroform is run off and after adjustment to pH 9.5 the aqueous phase is extracted with a further 10 ml of dithizone. The combined extracts are washed with 50 ml of dilute ammonia. To the organic phases is added 50 ml of 0.2 M-hydrochloric acid. The phases are separated and the aqueous portion washed with 5 ml of chloroform. The aqueous portion is evaporated to dryness and the residue dissolved in 5 ml of 2 M hydrochloric acid (solution A). Perchloric acid (3 ml) is added to the organic portion, evaporated to dryness, and a further 2 ml of 60% perchloric acid added to ensure that all organic matter has been... 

Preparation of Coal and Fly Ash for Isotope Dilution Analysis. Separate aliquots of coal and fly ash are weighed out and spiked with 204Pb and 233U, respectively. The chemical treatment and extraction of lead and uranium from coal and fly ash are identical, except coal is ashed at 450 °C before chemical treatment. The samples are dissolved with a mixture of hydrofluoric, nitric, and perchloric acids in Teflon beakers. The lead is separated by dithizone extraction, evaporated to dryness, redissolved in dilute nitric acid, and 10 ng are loaded on filaments with silica gel for mass analysis. 

In the radiochemical procedure the irradiated coal sample and mercuric oxide carrier are digested with sulfuric acid, followed by nitric acid. Water and potassium bisulfate are added to drive off any nitric acid remaining. The mercury is separated by a standard dithizone extraction, and the extract is counted for the 0.077 MeV photopeak of 197Hg with the Nal detector. 

Dithizone Extraction Solution On the day of use, dilute 30 mL of Dithizone Stock Solution to 100 mL with chloroform. 

A ammonium hydroxide or 1 10 nitric acid, using a pH meter, and return the solution to the separator. Add 5.0 mL of Dithizone Extraction Solution, and shake vigorously for 1 min. Allow the layers to separate, insert a plug of cotton into the stem of the separator, and collect the dithizone extract in a test tube. Determine the absorbance of each solution in 1-... 

Procedure (Note Refer to Lead Limit Test, Appendix TTTR, for the solutions and the control.) Add 3 mL of Ammonium Citrate Solution and 0.5 mL of Hydroxylamine Hydrochloride Solution to the Sample Solution, and make the combined solutions alkaline to phenol red TS with ammonium hydroxide. Add 10 mL of Potassium Cyanide Solution. Immediately extract the solution with successive 5-mL portions of Dithizone Extraction Solution, draining off each extract into another separator, until the last portion of dithizone solution retains its green color. Shake the combined extracts for 30 s with 20 mL of 1 100 nitric acid, and discard the chloroform layer. Add exactly 4 mL of Ammonia-Cyanide Solution and 2 drops of Hydroxylamine Hydrochloride Solution to the acid solution. Add 10 mL of Standard Dithizone Solution, and shake the mixture for 30 s. Filter the chloroform layer through an acid-washed filter paper into a Nessler tube, and compare the color with that of a standard prepared as follows Add 0.25 mL of the Standard Lead Solution containing 10 p,g/mL of lead (Pb) ion, 4 mL of Ammonia-Cyanide Solution, and 2 drops of Hydroxylamine Hydrochloride Solution to 20 mL of 1 100 nitric acid, and shake for 30 s with 10 mL of Standard Dithizone Solution. Filter through an acid-washed filter paper into a Nessler tube. The color of the Sample Solution does not exceed that in the control. 

Dithizone Extraction Solution Dissolve 30 mg of dithizone in 1000 mL of chloroform, add 5 mL of alcohol, and mix. Store in a refrigerator. Before use, shake a suitable volume of the solution with about half its volume of 1 100 nitric acid, discarding the nitric acid. Do not use if more than 1 month old. 

Potassium Cyanide Solution Dissolve 50 g of potassium cyanide in sufficient water to make 100 mL. Remove the lead from the solution by extraction with successive portions of Dithizone Extraction Solution as described under Ammonium Citrate Solution, then extract any dithizone remaining in the cyanide solution by shaking with chloroform. Finally, dilute the cyanide solution with sufficient water so that each 100 mL contains 10 g of potassium cyanide. 

Diluted Dithizone Extraction Solution Just before use, dilute 5 mL of Dithizone Extraction Solution with 25 mL of chloroform. 

An equation of the form of (23-32) has been derived and verified experimentally for the dithizone extraction of zinc. This equation may be derived by writing the equilibrium constant as the extraction constant of the reaction... 

Yamane, Y., Miyazaki, M., Iwase, H., Muramatsu, S. Analysis of metals in water. I. Detection of metals by dithizone extraction and thin-layer chromatography. Eisei Kagaku 13,... 

Food (total) Digestion of sample with HNOs and H2S04 under reflux isolation of mercury by dithizone extraction Colorimetric dithizone method No data No data AOAC 1984 (methods 25.138-25.145)... 

Precipitation of cadmium as the sulphide at low acidity (pH 1.5) allows traces of cadmium to be separated from large quantities of zinc. A small amount of sodium sulphide is added to the solution to precipitate cadmium, other Group II metals, and some of the zinc, which acts as a collector. Further separation from zinc can be achieved by a dithizone extraction. Precipitation of Cd in the presence of KCN allows its separation from Cu. In all... 

When a solution (pH 9) containing fairly large amounts of cyanide and citrate is shaken with dithizone in chloroform, indium passes into the chloroform layer accompanied only by Pb, Bi, Sn(II), and Tl. Bismuth may be isolated first by dithizone extraction at pH 3-4. Dithizone in CCI4 extracts In, but not Tl, from a solution at pH 5-6 [13]. 

In the presence of cyanide, dithizone extracts Pb together with Bi, Tl(l), and In. However, indium ions are extracted by dithizone in CCI4 from only weakly alkaline media. If the pH of the solution is 10 (as is commonly the case in the determination of Pb), indium remains in the aqueous phase. 

Dithizone extracts Ag from solutions containing chloride but at pH values of 2-5. In the presence of EDTA (pH 4-5) Ag (and also Hg and Au) can be extracted from a solution containing considerable amounts of Cu, Bi, Cd, Zn, Ni, and Pb. When a solution containing Ag, Au, and EDTA at pH 4.7 is heated to boiling, the gold is reduced by EDTA to the element. Mercury can be volatilized by igniting the sample before the determination of silver. 

Nielsen, Kudsk F. (1965) Determination of mercury in dithizone extracts by ultra-violet photometry. Scand. J. Clin. Lab. Invest., 17,171-177. 

Canney and Nowlan (47) have shown that the amount of dithizone-extractable heavy metals removed from stream sediments with ammonium citrate-hydroxylamine hydrochloride was linearly related to the amount of manganese dissolved. This indicates that the cobalt is present in the manganese oxides. In accordance with this data, it has been found that the slope of plots of the extraction rate vs, time (with dithionite-citrate) for cobalt from < 60 mesh fraction of Whiteoak Creek sediment was closer to that of manganese than that of iron, indicating that more of the... 

Satisfactory correlations between extractable heavy metals and pH for a variety of soils are notoriously poor. Thome et al, (233) found no consistent correlations for Utah soils between pH 3.2 acetic acid plus 0.05N potassium chloride extractable or total zinc with pH (or organic matter content). They concluded that total zinc differentiated zinc-deficient soils as well as the extraction procedure used. Brown et al, (38) observed no correlation between soil pH and either response to zinc application or ammonium acetate-dithizone extractable zinc. Kanehiro (129) did not find a satisfactory relation between soil pH and acid-extractable zinc however, if his samples which were more acid than pH 5.5 are ignored then there is a tendency for acid-extractable zinc to decrease with soil pH. Furthermore, if surface and subsurface samples are segregated the relationship is improved. This may be because of the presence of greater amounts of organic matter in the surface horizon samples hence, the hydrous oxides and their occluded metals were more soluble. 

Combine the dithizone extracts containing the gold-coloured silver dithi-zonate and any traces of red-purple copper dithizonate in the separating funnel and rinse with 20 ml of 0.1 m sulphuric acid. Discard the sulphuric wash solution and shake the remaining organic solution three times, for 1... 

Now extract the silver a further 2 - times with 3-ml portions of dithizone solution II until the final extract remains green. Combine the dithizone extracts and wash twice with 0.01 m ammonium hydroxide solution. This... 

Figure 9 The extraction percentage versus pH diagram for some metal dithizonates extracted by carbon tetrachloride.

Since the spectrophotometric determination of Hg by means of di-thizone can be falsified by other heavy metals and oxidation products of the dithizone, it is best to purify the dithizone extract by TLC beforehand. The various metal dithizonates, dithizone and its oxidation products are separated from one another on the chromatogram. In particular the ubiquitous Cu-dithizonate can be separated. The spots of Hg-dithizonate may be scraped off, eluted and evaluated colorimetric-ally. The order of migration distances is ... 

Analytical method. In order to measure colorimetrically the bulk concentration of lead ion in the aqueous suspension of y-AI2O3 containing lead nitrate, the interfering particles were filtered with Millipore filter (Millipore Filter Corp. GSWP 04700 with pore size of 0.22 ym). The colorimetric determination of lead ion was performed at X = 510 nm by the dithizone extraction method. 

Monier Williams in an investigation on the determination of lead in foodstuffs, critically reviewed the methods available and suggested a combination of that by Allport and Skrimshire using wet oxidation with sulphuric and nitric acids and that by Francis, Harvey and Buchan, in which the dithizone-extracted lead is precipitated as sulphate. The latter procedure eliminates bismuth and the colour developed with ammonia from nitric acid digestion. Finally, the lead sulphate is dissolved in ammonium acetate and the lead determined colorimetrically as sulphide. The method is as follows ... 

Dithizone extraction solution. Extract 20 ml of a 0-1 per cent solution of diphenylthiocarbazone in toluene with two 50-ml portions of dilute ammonium hydroxide (50 ml of water containing 1 ml of strong ammonia... 

To the acid extract and washings add 5 ml of ammoniacal hydroxylamine hydrochloride solution (see above), a volume of dithizone extraction solution equal to that used in the initial extraction and 7 ml of toluene and shake the mixture vigorously for half a minute. Allow the layers to separate and reject the aqueous layer. Wash the toluene/dithi-zone layer once with 10 ml of water without shaking and reject the washings. 

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