Ammonium pyrrolidine dithiocarbamate APDC

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. 

Ammonium pyrrolidine dithiocarbamate (APDC). The reagent is a white to pale yellow crystalline substance and is commonly supplied in bottles which contain a piece of ammonium carbonate in a muslin bag. In this form it is stable for at least one year at temperatures below 30 °C, but the finely divided material exposed to the ordinary atmosphere is much less stable. 

The concentration of copper in the column eluent was determined by flame atomic absorption spectroscopy of samples which were preconcentrated with ammonium pyrrolidine dithiocarbamate (APDC) and methyl isobutyl ketone. The pH of the acidified sample was adjusted to pH 2.5-3.5 using 400 pi 8 M ammonium acetate (Chelex cleaned). 

Ammonium pyrrolidine dithiocarbamate (APDC) chelate coprecipitation coupled with flameless atomic absorption provides a simple and precise method for the determination of nanomol kg 1 levels of copper, nickel, and cadmium in seawater. With practice, the method is not overly time-consuming. It is reasonable to expect to complete sample concentration in less than 20 min, digestion in about 4 h, and sample preparation in another hour. Atomic absorption time should average about 5 min per element. Excellent results have been obtained on the distribution of nickel and cadmium in the ocean by this technique. 

Reagents. Solvent methyl isobufyl ketone (MIBK). Chelating agent ammonium pyrrolidine dithiocarbamate (APDC). Make up a 1% (m/v) solution of APDC in water. Prepare fresh daily. 

The most commonly used chelating agent in atomic spectroscopy is ammonium pyrrolidine dithiocarbamate (APDC). This reagent, which is normally used as a 1-2% aqueous solution, can be directly extracted with methylisobutyl ketone (MIBK) as the organic solvent. As APDC forms extractable metal complexes over a wide range of pH (Table 6.1), careful control of pH allows some degree... 

Table 6.1 Dependence of pH on the ability of ammonium pyrrolidine dithiocarbamate (APDC) to form complexes with various metals [3]...

APHA. 1985f. Determination of low concentrations of cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel, silver, and zinc by chelation with ammonium pyrrolidine dithiocarbamate (APDC) and extraction into methyl isobutyl ketone (MIBK)-method 303B. In Standard methods for the examination of water and wastewater. 16th ed. Washington, DC American Public Health Association, 160-162. 

Berman (1967) complexed mercury with ammonium pyrrolidine dithiocarbamate (APDC) in urine, blood, and other tissue samples treated with trichloroacetic acid. She extracted the complex into methylisobutyl ketone (MIBK), and reported a detection limit of about 10 /complexed with APDC, can be quantitively extracted into MIBK from hydrochloric acid (at least up to 6 M) and nitric acid (up to 1.5 M) solutions (Brooks et al., 1989). 

Buchet et al. (1982) combined wet ashing of the urine with nitric acid with cupferron-chelation and 4-methylpentan-2-one extraction. Cupferron gave the best results in comparison to ammonium pyrrolidine dithiocarbamate (APDC) and 5,7-dichloro-8- quinoli-nol (dichloroxine). 

Several methods have been reported for concentrating lead, cobalt, and nickel in blood, urine, brines, and water prior to final determination by atomic absorption. Sprague and Slavin (6) described a procedure for determining these elements plus copper, cadmium, iron, and manganese in concentrated potassium chloride solutions. The metals were chelated with ammonium pyrrolidine dithiocarbamate (APDC) and extracted with methyl isobutyl ketone (MIBK). It was reported that the optimum pH for the extraction was approximately 2.8. Berman (J) described a similar chelation-extraction procedure for determining lead in urine and blood. Burrell (2) developed a procedure for determining cobalt and nickel in natural waters by atomic absorption in which both metals are first coprecipitated with ferric chloride from ten liters of water. The separated precipitate is subsequently dissolved and made up to 100 ml. volume with hydrochloric acid and water so that the final pH of the solution is 2.5. The nickel and cobalt are then chelated with APDC and extracted with three 10 ml. volumes of MIBK. Three extractions are necessary to achieve complete recovery of the chelated cations. A detection limit of 0.3 fig. of nickel per liter and 0.15 fig. of cobalt per liter was found. 

The test element can be extracted into a smaller volume of organic solvent, with (in many cases) a ten- to hundred-fold gain in concentration. Methyl isobutyl ketone (MIBK) is one of the best materials for solvent extraction and aspiration into a flame. Ammonium 1-pyrrolidinecarbodithioate (APCD) is a commonly used extracting agent because it reacts with a large number of elements in acidic solution [this reagent is often referred to as ammonium pyrrolidine dithiocarbamate (APDC) in the literature]. 

Chromium(VI) can be quantitated without coprecipitation by forming a metal chelate. Method 7196A provides a procedure to prepare the diphe-nylcarbazone complex with Cr(VI) in an aqueous matrix. The method is not sensitive in that it is useful for a range of concentrations between 0.5 and 50 mg/L Cr. A more sensitive colorimetric method converts Cr(VI) to Cr(VI) chelate with ammonium pyrrolidine dithiocarbamate (APDC), followed by LLE into methyl isobutyl ketone (MIBK). The molecular structure for APDC is as follows ... 

Ammonium pyrrolidine dithiocarbamate (APDC), for example, is suitable for group extraction in water. It is added as a 2 % aqueous solution to the water sample, which should be set to pH 2 (5 ml to 1 litre of water sample). Repeat extraction with about 13 ml of chloroform each time until... 

Dissolve 1.0 g ammonium pyrrolidine dithiocarbamate (APDC) in water and make up to 100 ml. 

The adsorption step in ACSV is carried out at a carefully controlled potential as it determines the adsorption efficiency. In most cases, an adsorption potential is chosen which is slightly more positive ( 0.1 Vor more) than the reduction potential of the metal-ligand complex. Figure 6 shows the optimization of the deposition potential for the determination of Zn using ammonium pyrrolidine dithiocarbamate (APDC) as the AL. The optimal deposition potential for this method is —0.9 V, with the reduction... 

In international intercomparison programs for the determination of Cd-B and Cd-U, GFAAS was by far the most used method [49,57]. This was also concluded in a review about Cd-B [50]. Other methods used for Cd-B were flame atomic absorption spectrometry (FAAS) with Delves cup [51] or punched paper disk [52], and differential pulse anodic stripping voltammetry (DPASV) [53]. Other methods used for Cd-U were FAAS with Delves cup [51], flame atomic fluorescence spectrometry [58], and DPASV after wet digestion [59]. For Cd-U in the past many modifications of the GFAAS method existed, e.g., extraction with ammonium pyrrolidine dithiocarbamate (APDC) or another compound [60,64], with ammonium dihydrophosphate and Triton-X [61], with diammonium hydrophosphate and nitric acid [62], with water dilution or direct [54,63], and with nitric acid dilution [54,65-67]. 

Ammonium pyrrolidine dithiocarbamate (APDC) and diethylammonium diethyldithio-carbamate (DDDC) Prepare an aqueous solution, 1 % (m/v) of each, and purify the reagents by extraction with Freon or chloroform (two extractions of 5 mL each) until metal blanks are negligible. Store the APDCVDDDC solution at about 4 °C. The solution is stable for 3 days. 

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. 

Ammonium pyrrolidine dithiocarbamate (APDC) An aqueous solution containing 0.1 mol/L APDC is prepared by dissolution in pure water. Contaminating zinc is removed from this solution by extraction with a solvent such as trichlorotrifluoroethane, dichloro-methane or formaldehyde. The solvent itself is first cleaned by shaking with acid. 

---