Ammonium dithiocarbamate analysis

Trace metal analyses were performed using sample acidification, complex formation using ammonium dithiocarbamate (APDC), extraction with methylisobutylketone (MIBK), and analysis of extracts by flame atomic adsorption. Details of the method are given by Brooks, Presley, and Kaplan (29). 

Liquid-liquid extractions using ammonium pyrrolidine dithiocarbamate (APDC) as a metal chelating agent are commonly encountered in the analysis of metal ions in aqueous samples. The sample and APDC are mixed together, and the resulting metal-ligand complexes are extracted into methyl isobutyl ketone before analysis. 

Cabezon et al. [662] simultaneously separated copper, cadmium, and cobalt from seawater by coflotation with octadecylamine and ferric hydroxide as collectors prior to analysis of these elements by flame atomic absorption spectrometry. The substrates were dissolved in an acidified mixture of ethanol, water, and methyl isobutyl ketone to increase the sensitivity of the determination of these elements by flame atomic absorption spectrophotometry. The results were compared with those of the usual ammonium pyrrolidine dithiocarbamate/methyl isobutyl ketone extraction method. While the mean recoveries were lower, they were nevertheless considered satisfactory. 

Tseng et al. [69] determined 60cobalt in seawater by successive extractions with tris(pyrrolidine dithiocarbamate) bismuth (III) and ammonium pyrrolidine dithiocarbamate and back-extraction with bismuth (III). Filtered seawater adjusted to pH 1.0-1.5 was extracted with chloroform and 0.01 M tris(pyrrolidine dithiocarbamate) bismuth (III) to remove certain metallic contaminants. The aqueous residue was adjusted to pH 4.5 and re-extracted with chloroform and 2% ammonium pyrrolidine thiocarbamate, to remove cobalt. Back-extraction with bismuth (III) solution removed further trace elements. The organic phase was dried under infrared and counted in a ger-manium/lithium detector coupled to a 4096 channel pulse height analyser. Indicated recovery was 96%, and the analysis time excluding counting was 50-min per sample. 

The availability of strongly chelating extractant reagents for a number of metals has lead to the development of procedures in which the metal is extracted from minimally treated blood or urine and then quantified by atomic absorption analysis. The metals for which such extractions can be used include cobalt, lead, and thallium extracted into organic solvent as the dithiocarbamate chelate, and nickel extracted into methylisobutyl ketone as a chelate formed with ammonium pyrro-lidinedithiocarbamate. 

Tris(pyrrolidine dithiocarbamato-)—cobalt(III) chelate, the precipitate formed by adding ammonium pyrrolidine dithiocarbamate to cobalt(II) solutions, has been found to be a good matrix for preconcentrating lead and several other metals by co-precipitation. Concentration factors of 40 to 400 are available by the method. The analyte is co-precipitated on the Co-APDC from a litre of sample. The precipitate is filtered on a fine porosity glass sinter and redissolved in a small volume of 6 M nitric acid. The solution is then used for atomic absorption analysis. 

APDC = ammonium pyrroiidine dithiocarbamate Bq = Bequerei and 1 pCi = 0.37 Bq dpm = disintegration per minute and 1 pCi = 2.22 dpm EDTA = ethyienediaminetetraacetic acid Fi = fiow injection HPLC=high performance liquid chromatography ICP = inductively coupled plasma spectrometry INAA = instrumental neutron activation and analysis MS = mass spectrometry NAA = neutron activation analysis nM = nanomole or 10 of a mol... 

Another method that has been employed with some success to preconcentrate elements in natural water samples is co-precipitation. This relatively simple method offers the advantage of giving a fairly uniform deposit that can be collected easily. One of the earlier applications of this technique involved the use of iron hydroxide as a co-precipitant for the determination of Fe, Zn, and Pb in surface waters [56]. One of the more popular co-precipitants in use today is ammonium pynolidine dithiocarbamate (APDC). In the application of this method to the analysis of natural waters, detection limits in the range 0.4-1.2 ppb have been claimed for the elements V, Zn, As, Hg, and Pb [57]. Other co-precipitants have been described, including the use of iron dibenzyl dithiocarbamate for the determination of U at the ppb level in natural waters [58], zirconium dioxide for the determination of As in river water [59], and polyvinylpyrrolidone-thionalide for the determination of Fe, Cu, Zn, Se, Cd, Te, Hg, and Pb in waste and natural water samples [60]. The use of... 

After chelation with hexamethylene ammonium hexamethylene dithiocarbamate (HMDC), silver is extracted from formate-buffered solution with xylene-diisopropyl ketone and the organic extract is determined directly by means of atomic-absorption analysis (3.4.16.1),... 

A simple MLC procedure was described for the simultaneous determination of five dithiocarbamates (sodium iV-methyldithiocarbamate, sodium iY,iV-dimethyldithiocarbamate, ammonium tetramethylene-dithiocarbamate, sodium iY,iV-diethyl-dithiocarbamate and disodium ethylenebisdithiocarbamate) [3], which employed CIS or cyano columns and micellar solutions of CTAB-methanol buffered at pH 6.8 with 0.02 M phosphate. Pond-water samples were used to assess the potential of MLC in the analysis of environmental samples. For the analyses, pond water was filtered and passed through a CIS-bonded column to remove aromatic compounds. Resorcinol was added as an internal standard. A typical chromatogram is shown in Fig. 10.8. 

Filterable metal may be analysed directly by AAS. Except in highly polluted waters, the use of flameless techniques will be necessary and research has shown that reliable results are obtained only by use of the method of standard additions to minimize matrix interferences. The sensitivity of flame methods may be enhanced if the lead is preconcentrated by extraction with ammonium pyrolidine dithiocarbamate in methyl isobutyl ketone (APDC/MIBK). This also eliminates many interferences, but prior heating of the sample with acid may be necessary to release complexed lead [8]. The use of ASV for analysis of filterable lead in water is rather more complex than might appear at first sight, since ASV is only sensitive to labile (weakly-bound) lead, and not to that strongly bound in complexes. Reduction of the sample pH by addition of an appropriate acid may cause release of most of the lead enabling analysis to be carried out. In general, AAS is to be preferred. 

Ammonium pyrrolidine dithiocarbamate (APDC) was used early on to determine zinc in natural waters by CSV (van den Berg, 1984b), and the procedure has not (yet) been improved. APDC is a general complexing agent and it is therefore perhaps surprising that there are no major interferences. Analysis is at pH values 7-8.5. 

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