Molybdoarsenic acid

Molybdenum trisulfide, 3, 1431 Molybdoarsenates, 3, 1041 non-Keggin, 3, 1042 Molybdoarsenic acid liquid-liquid extraction, 1, 548 Molybdoborates, 3,1042 Molybdocerophosphoric add determination, 1, 548 Molybdoenzymes, 3, 1352 molybdenum site, 3,1391 Molybdogermanates, 3,1038 Molybdogermanic acid liquid-liquid extraction, 1, 548 Molybdoniobic acid... 

Arsenic, oxidised to As(V) (e.g. by evaporation to dryness with HNO3) is made to react in a suitably acid solution (0.1-0.3 M H2SO4) with ammonium molybdate to form the molybdoarsenic heteropoly acid. The molybdoarsenic acid is then reduced [the Mo(Vl) atoms linked with As(V) are reduced to a lower oxidation degree] and a blue reaction product, the arsenomolybdenum blue is formed. The absorbance is measured either in the aqueous solution, or after extraction into oxygen-containing organic solvent [29-33]. The reaction conditions are so selected that the unreacted molybdate ions are not reduced. 

Alternatively, arsenic may be extracted as molybdoarsenic acid, and the reducing agent may then be added to the organic phase [25]. 

Methods based on extractable associates of the reduced form of molybdoarsenic acid with Crystal Violet (e=3.1 10 ). Methyl Violet, Brilliant Green, or Malachite Green have also been applied [54]. 

The amplification method for arsenic is based on its extractive separation as molybdoarsenic acid and determination of Mo with Sulphonitrophenol S (e = 4.5 10 ) or zinc dithiol [56]. The molybdoarsenic acid, after extraction into a mixture of butyl acetate and ethanol, is decomposed, then Mo(VI) is reduced to Mo(Ul) in a Jones reducer, and finally Mo is oxidised to Mo(Vl) be means of Fe(Itl). The Fe(ll) produced in this reaction gives a coloured complex with ferrozine. The amplification factor is 36, and e=9.4 10 [57]. 

The separation of P(V) from other elements, in particular from Si, is often achieved by extracting phosphorus as a heteropoly acid from a slightly acidic solution of pH -1.4. Higher alcohols, esters, and ethers are suitable extractants [3-5]. By extraction with a mixture of butanol and chloroform, molybdophosphoric acid can be separated from molybdoarsenic acid [6]. Isobutyl acetate extracts molybdophosphoric acid, but not molybdosilicic acid, from a solution at pH 0.3-1.0. 

Phosphorus(V), Ge(IV), and As(V) which give yellow heteropoly acids, interfere. Before silicon is determined, Ge and As may be separated by volatilization or extraction of GeCU and AsCli. Molybdophosphoric and molybdoarsenic acids are separated from molybdosilicic acid by extraction with butyl acetate at pH 0.3-1.0. The extractive separation of silicon from P(V) and As(V) has been discussed [5,21]. Molybdosilicic acid has been extracted with TOA in toluene [22]. Ion-associates with basic dyes, e.g., Chrompyrazole have been floated with a mixture of toluene and acetone [23]. 

Molybdcnum(V) complexes magnetic behavior, 271 spectra, 251 Molybdoarsenic acid liquid-liquid extraction, 548 Molybdocerophosphoric acid determination, 548 Molybdogermanic acid liquid-liquid extraction, 548 Molybdoniobic acid liquid-liquid extraction, 548 Molybdophosphates ammonium salt in gravimetry, 534 Molybdosilicophosphoric acid liquid-liquid extraction, 548 Mononuclear compounds neutral... 

An automated method reported for the determination of cellulase activity is based on stopping the enzyme reaction at alkaline pH, dialysis, and determination of the reducing power of the diffusate by the spectrophotometric ferricyanide-molybdoarsenic acid reaction. ... 

Molybdogermanic, molybdoniobic, molybdoarsenic and molybdosilicophosphoric acids and other heteropolyacids have been used in liquid-liquid extraction procedures which also permit the resolution of mixtures.68 A comprehensive review has been published.69... 

The free acid has not been isolated, and the complex is very easily degraded. The only salts known are the slightly soluble K3[AsMoi204o] 6 H20 and the difficulty soluble (NH4)3[AsMo1204o] 6 H20. In solution, most polymolybdoarsenates are readily converted into dimeric 9-molybdoarsenate anions. With arsenic, these compound types are the most stable and best known heteropolymolybdates and tungstates. It has been shown recently that the 12-molybdoarsenate(V) anion is stable in 1 1 water dioxane solutions15. ... 

As(V) by the addition of aqueous iodine, followed by conversion to molybdoarsenate and reduction to molybdenum blue by boiling under reflux with a sulphuric acid solution of ammonium vanadate and hydrazine sulphate. The method is sufficiently sensitive to determine down to 3 fig of Lewisite per millilitre of sample. 

As(V) has been separated from a number of elements by extraction into butanol from acidic medium as the molybdoarsenic heteropoly acid [11]. This acid has been extracted with solutions of some high molecular-weight amines in 1,2-dichloroethane [12]. 

Other more or less specific but less important reagents are for unsaturated compoimds molybdoarsenate [111], tetranitromethane [111, 113], osmium tetroxide [111, 113), p-anfinodimethylaniline-SOg [111, 113] for phenols, the nitroso reaction (Boute reagent) and Feigl reagent [113] for o-diphenols, phloroglucinol and vanadic acid [113] for reactions of the side chain, the Porter-Silber reaction [111], methyl ketones and formaldehydogens [111] and further modified reactions usual in PC [129]. 

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