Silver Diethyldithiocarbamate Solution

Arsenic. Total arsenic concentration can be determined by reduction of all forms to arsine (AsH ) and collection of the arsine in a pyridine solution of silver diethyldithiocarbamate. Organoarsenides must be digested in acidic potassium persulfate prior to reduction. The complex that forms is deep red, and this color can be measured spectrophotometricaHy. Reduction is carried out in an acidic solution of KI—SnCl2, and AsH is generated by addition of 2inc. 

Merry and Zarcinas [33] have described a silver diethyldithiocarbamate method for the determination of arsenic and antimony in soil. The method involves the addition of sodium tetrahydroborate to an acid-digested sample which has been treated with hydroxylammonium chloride to prevent the formation of insoluble antimony compounds. The generated arsine and stib-ine react with a solution of silver diethyldithiocarbamate in pyridine in a gas washtube. Absorbance is measured twice at wavelengths of 600 and 504 nm. 

Reagents. Silver DDC Solution. A 0.5% solution of silver diethyldithiocarbamate in pyridine. This reagent should be stored in amber bottles. 

In a further method the sample is heated in a sealed tube for 5 min with a mixture (3 + 1) of magnesium and magnesium oxide, which converts all the arsenic into magnesium arsenide On decomposition by dilute sulphuric acid, arsine is evolved and is absorbed in a 0.5% solution of silver diethyldithiocarbamate (AgDDC) in pyridine. The colour produced has an absorption maximum at 560 nm and is proportional to concentration up to 20 fig of arsenic in 3 ml of solution. Alternatively, the arsine is oxidized by bromine and determined iodimetrically. 

Arsine bubbled into the solution in the cuvette, reacting with silver diethyldithiocarbamate to form a colored complex compound according to the following equation ... 

A 25-mL solution containing 500 ppb of arsenic (Ag3+) was stirred with 1 g of borohydride-form A-26 anion-exchange resin. The reaction vessel was connected to an absorption tube filled with a solution to absorb the volatile hydride of arsenic (i.e., arsine, AsH3). The absorption solution is made by dissolving 1 g of silver diethyldithiocarbamate (SDDC) in 200 mL of pyridine. The volatile arsine is complexed with the SDDC solution to give a colored solution, whose absorbance is... 

Gravimetric methods and chemical methods, such as colorimetric measurements based on the arsenic-molybdenum blue complex (1,2,3) and arsine generation in combination with silver diethyldithiocarbamate (4, 5, 6,7), have been used to measure arsenic in aqueous media. Various instrumental methods such as differential pulse polarography (8), heated vaporization atomic absorption (9), arsine generation in combination with atomic absorption spectroscopy (10, 11, 12) or non-dispersive atomic fluorescence spectroscopy (13), and optical emission spectroscopy (14) can be used to determine arsenic in aqueous solutions. 

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. 

Spectrophotometric determination. The airborne aerosol is filtered and after the filter mineralization, arsenic compounds are reduced with zinc in HCl medium to arsine. Arsine with a solution of silver diethyldithiocarbamate in pyridine yields a red colour, which is suitable for spectrophotometric determination. The measurement is made at 540 nm [26]. 

AsHs (hydrogen arsenide) reacts with a silver diethyldithiocarbamate [AgSC(S)N(Et)2] solution in pyridine to yield a soluble red complex. 

Selenium is extracted as diethyldithiocarbamate complex from the solution containing citrate and EDTA [5]. Ohta and Suzuki [6] found that only a few elements, such as copper, bismuth, arsenic, antimony, and tellurium, are also extracted together with selenium. They examined this for effects of hundredfold amounts of elements co-extracted with the selenium diethyldithiocarbamate complex. An appreciable improvement of interferences from diverse elements was observed in the presence of copper. Silver depressed the selenium absorption in the case of atomisation of diethyldithiocarbamate complex, but the interference of silver was suppressed in the presence of copper. The atomisation profile from diethyldithiocarbamate complex was identical with that from selenide. 

In the a-modifications of silver(I) diethyldithiocarbamate irregular hexamers are linked in chains by weak bonds only (Ag—-S = 299pm). Two of the six silver atoms have four-fold coordination, the others three-fold. Two ligands coordinate to only two metal atoms, the others to four. Five short metal-metal distances occur in each of the hexamers.323 In the /3-modification, which is a true high polymer, all the silver atoms have four-fold coordination and all the ligands are linked to three metal atoms, (39). There are only two short metal-metal distances per six silver atoms. Crystals of the /3-form were obtained from CS2 solutions cooled to -40 °C. Ag—S bond lengths were in the range 251-274 pm.324... 

Other methods for separating silver involve extraction of the diethyldithiocarbamate into chloroform [pH 4-11 (EDTA as masking agent)] [1]. The thiocyanate complex of silver can be extracted from 0.1-1 M solutions of H2SO4, HCl, or HCIO4 into TBP [2]. 

Silver compounds, available from commercial suppliers, are expensive. Reagent grades of silver(I) carbonate, cyanide, diethyldithiocarbamate, iodate, nitrate, oxide, phosphate, and sulfate are available. Standardized solutions of silver nitrate are also available for analytical uses. Purified grades of s ver(I) acetate, bromide, cyanide, and iodide can be purchased silver nitrate is also made as a USP XX grade for medicinal uses (6). 

Early crystallographic studies revealed the hexameric nature (R = Et, E r) (328,329) of silver(I) dithiocarbamate complexes in the solid state, although in solution they are believed to be in equilibrium with monomeric species (329). More recently, the diethyldithiocarbamate complex has been the subject of two further crystallographic studies (Fig. 241) (330,331). Delgado and Diez (329)... 

---