Acid-digestion/solvent-extraction

Munoz O, Velez D, Montoro R (1999) Optimization of the solubilization, extraction and determination of inorganic arsenic [As(III) i- As(V)] in seafood products by acid digestion, solvent extraction and hydride generation atomic absorption spectrometry. Analyst 124 601-607. 

The development of multimode reactors for organic synthesis occurred mainly from already available microwave acid-digestion/solvent-extraction systems. Instruments for this purpose were first designed in the 1980s and with the growing demand for... 

A common procedure for the analysis of nitrofuran metabolites involves hydrolysis of the protein-bound metabolites under acidic conditions followed by deriva-tization with 2-nitrobenzaldehyde (Eig. 7.5). After neutralization of the digest, solvent extraction is carried out with ethyl acetate. Residues are detected by LC-UV or LC-MS/MS In some cases an additional liquid-liquid extraction or solid-phase extraction step is applied to remove excessive matrix compounds. A broad overview of applied methods was published by Vass et al. in 2008. ... 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Hydrochloric acid digestion takes place at elevated temperatures and produces a solution of the mixed chlorides of cesium, aluminum, and other alkah metals separated from the sUiceous residue by filtration. The impure cesium chloride can be purified as cesium chloride double salts such as cesium antimony chloride [14590-08-0] 4CsCl SbCl, cesium iodine chloride [15605 2-2], CS2CI2I, or cesium hexachlorocerate [19153 4-7] Cs2[CeClg] (26). Such salts are recrystaUized and the purified double salts decomposed to cesium chloride by hydrolysis, or precipitated with hydrogen sulfide. Alternatively, solvent extraction of cesium chloride direct from the hydrochloric acid leach Hquor can be used. 

Cesium isotopes can be recovered from fission products by digestion in nitric acid, and after filtration of waste the radioactive cesium phosphotungstate is precipitated using phosphotungstic acid. This technique can be used to prepare radioactive cesium metal or compounds. Various processes for removal of Cs isotopes from radioactive waste have been developed including solvent extraction using macrocycHc polyethers (62) or crown ethers (63) and coprecipitation with sodium tetraphenylboron (64). 

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used. 

Conventional techniques such as solvent extraction followed by gas chromatography mass spectrometry (GCMS), and acid digestions followed by GCMS have all been performed on meteorite samples but all information about the location within the sample is lost during a digestion processes. However, microprobe laser desorption studies allow the profiling of material within the meteorite sample. 

Sample dissolved by alkali and acid digestion, cleaned up by solvent extraction. 

There are several processes for commercial thorium production from monazite sand. They are mostly modifications of the acid or caustic digestion process. Such processes involve converting monazite to salts of different anions by combination of various chemical treatments, recovery of the thorium salt by solvent extraction, fractional crystallization, or precipitation methods. Finally, metalhc thorium is prepared by chemical reduction or electrolysis. Two such industrial processes are outlined briefly below. 

Uranium dioxide occurs in mineral uraninite. Purified oxide may be obtained from uraninite after purification. The commercial material, however, also is recovered from other uranium sources. Uranium dioxide is obtained as an intermediate during production of uranium metal (See Uranium). Uranyl nitrate, U02(N03)2, obtained from digesting the mineral uraninite or pitchblende with concentrated nitric acid and separated by solvent extraction, is reduced with hydrogen at high temperatures to yield the dioxide. 

Ytterbium oxide is produced as an intermediate in recovering ytterbium from minerals (See Ytterbium). After opening the ore by digestion with concentrated sulfuric acid or caustic soda solution at high temperatures, rare earths are separated by ion exchange, solvent extraction, or fractional precipitation. Ytterbium fraction is treated with oxahc acid or sodium oxalate to precipitate jdterbium oxalate, which is ignited to yield ytterbium oxide. 

Developments of recent years include plants designed to precipitate the calcium sulfate in the form of the hemihydrate instead of gypsum, hi special cases, hydrochloric acid is used instead of sulfuric acid for rock digestion, the phosphoric acid being recovered in quite pure form by solvent extraction. Solvent-extraction methods have also been developed for the purification of merchant-grade acid, which normally contains impurities amounting to 12 18% of the phosphoric acid content. Processes for recovering part of the fluorine in the phosphate rock are in commercial use. 

Thompson and Zao [170] have described a solvent extraction-inductively coupled plasma atomic emission spectrometric method for the determination of down to 0.02 - 0.03 xg/g of molybdenum in soils. The soil sample is pressure-leached with 6 M hydrochloric acid and at 120 °C for 15 minutes. The digest is then extracted with heptan-2-one to separate molybdenum from potentially interfering elements such as iron, aluminium, calcium and magnesium. This organic extract is then directly sprayed into an inductively coupled plasma atomic emission spectrometer operated at 1.65 to 1.7 kW power. 

It should be noted that microwave-assisted extraction (MAE) discussed in this chapter is different from microwave-assisted acid digestion. The former uses organic solvents to extract organic compounds from solids, while the latter uses acids to dissolve the sample for elemental analysis with the organic contents being destroyed. Microwave-assisted digestion of metals is covered in Chapter 5. 

The filtered sample is neutralized with ammonia, and then buffered sodium diethyldithiocarbamate (SDDC) is added. The pH is adjusted to approximately 6, and the sample, in a separatory funnel, is shaken thoroughly. The analyte is then extracted twice with organic solvent. Nitric acid is added to the solvent, and it is evaporated to dryness on a hotplate. The residue is taken up in nitric and hydrochloric acids, and the dissolved residue is analyzed by AAS. It should be noted that the soluble metals are those that pass through the 0.45-pm filter, while total metals do not include those that are so tightly bound into the particles filtered out that they were not solubilized in the slow, mild acid leaching process to which the sample was exposed. For a true total metal analysis, an acid digestion would be required. 

Dissolution and Extraction in General For the dissolution of fish tissues different procedures are reported. Acid or alkaline digestion or solvent extraction is usually used for the separation of Hg species from biological matrices [45, 46]. For the quantitative extraction of Hg, four methods were examined HC1 leaching, alkaline-methanol extraction with tetramethylammonium hydroxide (TMAH) and... 

Related applications include peptide/protein hydrolysis, heterogeneous catalysis reactions, acid digestion of samples, (e.g. tissue, implants, catalysts, drugs, etc), for AA / ICP / ICP-MS analysis, solvent extractions, processing and/or destruction of toxic chemicals, chemotherapy and anti-neoplastic agents. 

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