DEVARDA’S ALLOY

With a nitrate in alkaline solution, ammonia is evolved quantitatively by Devarda s alloy (Al, 45% Cu, 50% and Zn, 5%). This reaction can be used to estimate nitrate in absence of ammonium ions (see below) ... 

By the evolution of ammonia with Devarda s alloy in alkaline solution in absence of ammonium ions this is used quantitatively, the ammonia being absorbed in excess standard acid and the excess acid back-titrated. 

Inorganic analytes that are neutral in aqueous solutions may still be analyzed if they can be converted to an acid or base. For example, N03 can be quantitatively analyzed by reducing it to NH3 in a strongly alkaline solution using Devarda s alloy, a mixture of 50% w/w Cu, 45% w/w Al, and 5% w/w Zn. 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

Devarda s Method. Nitrogen in nitrates or nitric acid also may be deterrnined by the Kjeldahl method or by Devarda s method. The latter is both convenient and accurate when no organic nitrogen is present. The nitrate is reduced by Devarda s alloy to ammonia in an alkaline solution. The ammonia is distilled and titrated with standard acid. 

In the laboratory NH3 is usually obtained from cylinders unless isotopically enriched species such as NH3 or NDj are required. Pure dry can be prepared by treating an enriched NH salt with an excess of KOH and drying the product gas over metallic Na. Reduction of NOs or with Devarda s alloy (50%... 

Discussion. Nitrates are reduced to ammonia by means of aluminium, zinc or, most conveniently, by Devarda s alloy (50 per cent Cu, 45 per cent Al, 5 per cent Zn) in strongly alkaline solution ... 

The reagent is employed for the determination of ammonia in very dilute ammonia solutions and in water. In the presence of interfering substances, it is best to separate the ammonia first by distillation under suitable conditions. The method is also applicable to the determination of nitrates and nitrites these are reduced in alkaline solution by Devarda s alloy to ammonia, which is removed by distillation. The procedure is applicable to concentrations of ammonia as low as 0.1 mgL-1. 

Devarda s alloy 303, 679 Deviation mean (average), 134 standard, 134... 

Analytical. Mannitol Hexanitrate can be hydrolyzed in basic soln and the soln acidified in the presence of NITRON to quanty ppt NITRON nitrate (Ref 16). A procedure is described for. the quant detn of nitrate esters, including Mannitol Hexanitrate, in the presence of aromatic nitro compds in Ref 17. It gives a yellow color when treated in et ale or acet with 5% aq K hydroxide, then 5% aq ammonia (Ref 24), It can be quanty detd by reduction with Devarda s alloy (Encycl 5, D-l 110) or A1 wire in aq et ale and titration of the evolved... 

A method of analysis based on converting nitrate groups to ammonia with Devarda s alloy is described by Smeenk (Ref 103). PETN is dissolved in ethanol and the ammonia formed is titrated with standard acid soln... 

During preparation of an oxidising agent on a larger scale than described [1], addition of warm sodium hydroxide solution to warm ammoniacal silver nitrate with stirring caused immediate precipitation of black silver nitride which exploded [2], Similar incidents had been reported previously [3], including one where explosion appeared to be initiated by addition of Devarda s alloy (Al—Cu—Zn) [4], The explosive species separates at pH values above 12.9, only produced when alkali is added to ammoniacal silver solutions, or when silver oxide is dissolved with ammonia [5], The Sommer Market reagent mixture used to identify cellulose derivatives led to a severe explosion [6],... 

Aluminium-copper-zinc alloy (Devarda s alloy)... 

The Department of the Environment UK [155] has described a number of alternative methods for the determination of total oxidised nitrogen (nitrate and nitrite) in aqueous solution, while specific methods for nitrate and nitrite are also included. Among the methods for total oxidised nitrogen, one is based on the use of Devarda s alloy for reduction of nitrate to ammonia, and another uses copperised cadmium wire for reducing nitrate to nitrite, which is determined spectrophotometrically. Nitrate may also be determined spectrophotometrically after complex formation with sulfosalicylic acid or following reduction to ammonia, the ammonia is eliminated by distillation and determined titrimetrically. Other methods include direct nitrate determination by ultraviolet spectrophotometry, measurements being made at 210 nm, and the use of a nitrate-selective electrode. Details of the scope, limits of detection, and preferred applications of the methods are given in each case. 

DEVARDA S ALLOY DIAZONIUM TETRAHALOBORATES ISOXAZOLES NITROBENZALDEHYDES NITROBENZYL COMPOUNDS... 

ALKALI-METAL ALLOYS, ALKALI METALS DEVARDA S ALLOY, FERROALLOY POWDERS FINELY DIVIDED METALS, LANTHANIDE METALS LIGHT ALLOYS, METAL DUSTS METAL FIRES, MILD STEEL... 

There are two approaches to the analysis. In the first, the extractable ammonium-N is determined by a Kjeldahl distillation, and this is subtracted from the value for ammonium plus nitrate (and nitrite) determined by a further separate Kjeldahl distillation preceded by reduction with nascent hydrogen produced by the reaction of Devarda s alloy (45% Al, 50% Cu, 5% Zn) in strongly alkaline solution ... 

The second, quicker, way is simply to add the Devarda s alloy to the distillation flask after the first distillation, and then redistil the ammonia produced from the reduced nitrate - this is described below. 

Procedure. Pipette 5 ml nitrate-N standard solution into the distillation flask, add 1 drop octan-2-ol, approximately 0.5 g Devarda s alloy, 6 ml magnesium hydroxide suspension (or 0.5 g MgO), and steam-distil the ammonia into 5-ml boric acid solution in a 100-ml conical flask. After approximately 40 ml distillate has been collected over a 5-min period, wash the tip of the condenser into the distillate, add 2-3 drops mixed indicator solution and titrate with 0.005 M HjSO until the colour changes from green to purple. Carry out a blank distillation using 5 ml water instead of extract solution and subtract from the standard titration to give a difference of 5.0 ml. 

After determination of extractable ammonium-N (5.4b.i), add approximately 0.5 g Devarda s alloy and distil as above. Adjust the size of the aliquot of extract if the titre lies outside the range 0.2-7.0 ml. 

Water extraction or dilution of fresh material. Alkaline steam distillation with Devarda s alloy after removal of ammonium N. Final measurement by titration. 

Kjeldahl Method. A method of detg the N in an organic compd by digesting the substance with coned sulfuric acid in the presence of catalysts such as selenium, Devarda s alloy, etc. This treatment transforms the N into Amm sulfate. By adding an excess of caustic and distg the liberated ammonia into a measured quantity of standard sulfuric acid (which is later titrated), it is possible to determine the amount of N in the substance... 

H2Oz was added 5 times after an interval of 5mins. The mixt was cooled and 1 drop of 1% Osmium Tetraoxide soln was added to decomp excess H202. Three hundred mg of Devarda s alloy was added and the flask quickly connected to a steam distilling app. The distillate entered 25ml N/70 HC1. Steam distillation was commenced after the H2 evolution ceased. 

By using Devarda s alloy (45% Al, 5% Zn, 50% Cu) in alkaline solution, nitrates are reduced to ammonia. The ammonia can be identified using damp indicator paper, which turns blue. 

Devarda s alloy, see Aluminium—copper—zinc alloy, 0050... 

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