Ammonium 12-molybdate, test reagent

Acidify the soda extract with dilute hydrochloric acid, pass in sulphur dioxide to reduce the arsenate to arsenite, boil off the excess sulphur dioxide (test with potassium dichromate paper), and pass hydrogen sulphide into the solution to precipitate the arsenic as arsenic(III) sulphide continue the passage of hydrogen sulphide until no more precipitate forms. Filter, boil off the hydrogen sulphide, and test the filtrate for phosphate by the ammonium molybdate test or with the magnesium nitrate reagent. 

Arsenate, (i) Action of H2S on acid solution (III.13, 1), and silver nitrate solution test upon neutral solution (III.13, 2). (ii) Magnesium nitrate reagent test (ffl.13, 3). (iii) Ammonium molybdate test (III.13, 4). 

It is usually preferable to oxidise the compound directly as follows. Intimately mix 0 02-0 05 g. of the eompound with 3 g. of sodium peroxide and 2 g. of anhydrous sodium carbonate in a niekel erucible. Heat the crueible and its eontents with a small flame, gently at first, afterwards more strongly until the eontents are fused, and eontinue heating for a further 10 minutes. Allow to stand, extract the contents of the crucible with water, and filter. Add exeess of eoneentrated nitrie acid to the filtrate and test with ammonium molybdate reagent as above. A yellow preeipitate indicates the presenee of phosphorus. It must be borne in mind that the above treatment 1 eonvert any arsenie present into arsenate. 

Modras (51) reported spot test reactions to differentiate hydralazine from closely related drugs. Reagents used were aqueous copper (I) chloride, aqueous ammonium molybdate, iodine in potassium iodide solution, aqueous cobalt (II) nitrate, alcoholic ninhydrin, and alcoholic bromophenol blue. The tests were performed on paper or on Silica Gel G. 

The ester group is then hydrolysed, and the hydrolysis normally stops at the MePO(OH)2 stage. More vigorous conditions are required to rupture the Me—P bond. Thus the normal hydrolysis product of D.F.P. and of tabun, namely, phosphoric acid, will give a positive test with ammonium molybdate, whereas the product from sarin, namely, methylphosphonic acid, will not respond to this test. Vigorous reagents such as hot nitric acid and ammonium persulphate will break the C—P link and then a positive test for phosphate is obtained with ammonium molybdate. Sarin can be prepared in a variety of ways. Three... 

The limit test for phosphate is based upon the formation of ayellow colour reaction with molybdovanadic reagent (combination of ammonium vanadate and ammonium molybdate) in an acidic medium. However, the exact composition of the molybdovanadophosphoric acid complex is yet to be established. 

Test for phosphorus. The presence of phosphorus may be indicated by a smell of phosphine during the sodium fusion and the immediate production of a jet-black colour when a piece of filter paper moistened with silver nitrate solution is placed over the mouth of the ignition tube after the sample has been dropped on the hot sodium. Treat 1.0ml of the fusion solution with 3ml of concentrated nitric acid and boil for 1 minute. Cool and add an equal volume of ammonium molybdate reagent (3). Warm the mixture to 40-50 °C, and allow to stand. If phosphorus is present, a yellow crystalline precipitate of ammonium 12-molybdophosphate, (NH4)3[PMo12C>4o], will separate. 

Phosphate Evaporate 400 mg of sample to dryness on a steam bath. Dissolve the residue in 25 mL of approximately 0.5 N sulfuric acid, add 1 mL of ammonium molybdate solution [500 mg of (NH4)5Mo7024 4H20 in each 10 mL of water] and 1 mL of p-methylaminophenol sulfate TS, and allow it to stand for 2 h. Any blue color does not exceed that produced by 2.0 mL of Phosphate Standard Solution (20 pig PO4) (see Solutions and Indictors) in an equal volume of solution containing the quantities of the reagents used in the test. Residue on Evaporation Evaporate 25 g of sample to dryness in a tared porcelain or silica dish on a steam bath, and... 

The spot-test technique of the reaction utilizes the conversion of the silicic and fluosilicic acids by means of ammonium molybdate into silicomolybdic acid H4[SiMo12O40]. The latter, unlike free molybdic acid, oxidizes benzidine in acetic acid solution to a blue dyestuff and molybdenum blue is simultaneously produced. (DANGER THE REAGENT IS CARCINOGENIC.)... 

Mix the solid test sample with a little pure silica powder in the tube of the apparatus shown in Fig. 11.53 and moisten the silica with 1-2 drops concentrated sulphuric acid. Place a drop of water on the glass knob of the stopper, insert it in position and heat the apparatus gently for about 1 minute. Remove the source of heat and allow to stand for 5 minutes. Wash the drop of water into a micro crucible, add 1-2 drops ammonium molybdate reagent and warm the mixture until bubbling just commences. Allow to cool, introduce a drop of a 005 per cent solution of benzidine in 2m acetic acid and a few drops of saturated sodium acetate solution. A blue colour is obtained. 

Ammonium molybdate-benzidine test (DANGER THE REAGENT IS CARCINOGENIC.) Silicates react with molybdates in acid solution to form the complex silicomolybdic acid H4[SiMo12O40]. The ammonium salt, unlike the analogous phosphoric acid and arsenic acid compounds, is soluble in water and acids to give a yellow solution. The test depends upon the reaction between silicomolybdic acid and benzidine in acetic acid solution whereby molybdenum blue and a blue quinonoid oxidation compound of benzidine are produced. 

Ammonium molybdate-benzidine test (DANGER THE REAGENT IS... 

CARCINOGENIC.) In this test use is made of the fact that benzidine, which is unaffected by normal molybdates and by free molybdic acid, is oxidized in acetic acid solution by phosphomolybdic acid or by its insoluble ammonium salt (see reaction 4 above). This reaction is extremely sensitive two coloured products are formed, viz. the blue reduction product of molybdenum compounds ( molybdenum blue ) and the blue oxidation product of benzidine ( benzidine blue ). Moreover, solutions of phosphates which are too dilute to show a visible precipitate with the ammonium molybdate reagent will react with the molybdate reagent and benzidine to give a blue colouration. 

Place a drop of the acid solution under test upon quantitative filter paper, add a drop of the ammonium molybdate reagent, followed by a drop of 0-05 per cent benzidine acetate. Hold the paper over ammonia vapour. A blue stain is formed when most of the mineral acid has been neutralized. 

Test 0-5 ml of the filtrate (or solution, if silicate is absent) for phosphate with 3 ml ammonium molybdate reagent and a few drops of concentrated HN03, and warm to about 40°C a yellow ppt. indicates phosphate is present. If phosphate is present (9), remove all phosphate ions as detailed in Tables V.20-V.22 (Section V.13). 

Arsenite. (i) Action of H2S upon acid solution (III. 12, 1). (ii) Silver nitrate solution test (III. 12, 2), and absence of precipitate with magnesium nitrate reagent (III.12, 3) or on boiling with ammonium molybdate solution and nitric acid, (iii) Bettendorff s test (III.12, 6). 

Test for Phosphorus.—One cubic centimeter of the original solution from the fusion is boiled for 1 minute with 3 cc. of concentrated nitric acid. This treatment oxidizes the sodium phosphide to sodium phosphate. The presence of the latter is tested for by adding to the cooled solution twice its volume of ammonium molybdate reagent. The tube is heated to such a temperature that it can just be held in the hand, and is then set aside. The formation of a yellow precipitate indicates phosphorus, provided arsenic is not present. 

Prepare a silica reagent by mixing equal volumes of 10 per cent ammonium molybdate and 5M nitric acid. Put 1 ml of the silica sol in one tube and 1 ml of silicate solution in another dilute both with 20 ml of water, and add 1 ml of silica reagent. Yellow silicomolybdic acid forms in both tubes, but it is much more intense in the. silicate solution. A fresh silica sol cannot be distinguished from a silicate solution by this test, though their reactions to litmus are quite different. 

The test described on page 388 may be applied for the rapid detection of phosphates in rocks and minerals. A few milligrams of the powdered rock or a splinter of the solid are placed on filter paper, moistened with a drop of ammonium molybdate solution, and held over a flame for a short time. A drop of benzidine acetate solution is added and the moist fleck held over ammonia. A brilliant blue forms on the paper either at or near the position of the sample, sometimes in continuous patches, and wherever traces of ammonium phosphomolybdate have been formed. A useful procedure is to carry out the test on a streak plate. The reagents are applied to the streak. 

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