Ammonium chloride phosphomolybdate

This ammonium phosphomolybdate complex is yellow, but if mildly reduced by ascorbic acid in the presence of potassium antimonyl tartrate a solution of stable bluish-purple color ( molybdenum blue ) develops after about ten minutes, which has its strongest absorption at 882 pm (Fig. 4.6). Other mild reducing agents have also been used, including tin(II) chloride, or hydrazine sulfate, which give maximum absorbances at slightly different wavelengths. The intensity of the color which develops is linearly proportional to the... 

If the water is first concentrated to one-fiftieth of its bulk, tests may be carried out for magnesia and phosphates. The former is precipitated as magnesium ammonium phosphate on standing for some twenty-four hours after addition of sodium phosphate solution to the water rendered alkaline with ammonium hydroxide in the presence of chloride. It is assumed that any lime has previously been removed with ammonium oxalate. Phosphates are precipitated as yellow phosphomolybdate on adding excess of ammonium molybdate solution to the water acidified with nitric acid, and warming. 

The precipitates obtained with magnesia mixture (magnesium chloride in ammoniacal solution), or ferric chloride in an acid solution to which sodium acetate has been added, are often used as tests for phosphate (see p. 180), and in the latter case the phosphate is removed from solution as ferric phosphate. Another common test is the formation of yellow ammonium phosphomolybdate when, a nitric acid solution of ammonium molybdate is added to phosphate solution (see pp. 180, 181). 

Tin(II) chloride reduces not only the reactive phosphomolybdic acid but also its relatively unreactive (e.g. ammonium or potassium) salts to molybdenum blue . However, antimony(III) salts do not reduce ammonium phos-phomolybdate Sn2+ may thus be detected in the presence of Sb3+. 

Many reducing agents have been used for producing the blue phosphomolybdate complex, including aminonaph-tholsulfonic acid, stannous chloride, methyl-p-aminophenol sulfate, ferrous ammonium sulfate, ascorbic acid, and N phenyl-p-phenyldiamine (semidine) Each of these... 

If higher sensitivities are desired then the ammonium phosphomolybdate product may be reduced with stannous chloride or ascorbic acid in order to give soluble molybdenum blue [24]. Spectrophotometric determination of the blue absorbance at 885 nm gives a detection limit of 0.003 mg/L phosphate, stated as phosphorus (3 ppb in freshwater) or 0.0092 mg/L as expressed phosphate [24]. 

Orthophosphate. The method used on San Francisco Bay water is a modification of the technique suggested by the AASGP (2) in which a membrane-filtered sample reacts with ammonium molybdate in acid solution and the resulting phosphomolybdic acid complex is extracted into an isoamyl alcohol/benzene mixture. Stannous chloride is used to reduce the extracted phosphomolybdic acid to molybdenum blue which is measured colorimetrically. 

In the second step, the reductant stannous chloride (tin(II) chloride) is added to the solution. The yellow ammonium phosphomolybdate is thereby reduced to a substance called molybdenum blue. The structure of this amorphous substance of ammonium, phosphate, and molybdate has not been elucidated, but the corresponding molybdate blue is presented with the formula [Mo03]i54(H20)7o]y. ... 

Ammonium thiosulfate Copper chloride (ic) Phosphomolybdic acid Phosphotungstic acid Potassium ferricyanide Sodium ferrocyanide Sodium silicomolybdate Sodium thiosulfate anhydrous Sodium thiosulfate pentahydrate fixative, photographic developer Sodium sulfite... 

Cupric sulfate anhydrous Cupric sulfate pentahydrate Direct brown 95 Ferric ammonium ferrocyanide Ferric chloride Ferric chloride hexahydrate Ferric sulfate Lead chromate oxide Lead molybdate Mercury sulfide (ic), black Mercury sulfide (ic), red Molybdenum trioxide 3-Naphthol Nonoxynol-55 Phosphomolybdic acid... 

Ammonium citrate tribasic Ammonium fluoborate Ammonium-12-molybdosilicate Ammonium phosphomolybdate Basic blue 9 Bromodichloromethane t-ButyIdimethylsilyl imidazole Chromium chloride (ous) Dimethyl acetamide Dimethyl formamide Ethoxydiglycol acetate Ethyl acetate Ethylbenzene Ethyl formate Ferric sulfate Formic acid Heptane Hexamethylenetetramine Isopropyl ether Methyl cyclohexane 2,7-Naphthalenediol ... 

Molybdenum blue Phosphate ions react with molybdate to form ammonium phosphomolybdate, which is reduced to convert it to molybdenum blue. Tin(II) chloride and ammonium iron(II) sulfate are used as reducing agents. 

Some of the innumerable reagents used in TEC are based on reactions with more or less well-established mechanism. Eor example, sodium iodobismuthate (Dragendorff reagent) is widely used among others for alkaloids and quaternary ammonium compounds, 4-dimethylaminobenzaldehyde for primary amines and amino acids, 2,4-dinitrophenylhydrazine for aldehydes and ketones, ninhydrin for amino acids and some antibiotics, fluorescamine for primary and secondary amines, phosphomolybdic acid for lipids, various steroids, and other compounds, chlorine vapor followed by Kl/starch for amines and amides. More complex is the mechanism of the reactions with some other reagents, containing high concentrations of sulfuric acid, vanillin/sulfuric acid, phosphoric acid, aluminum chloride, antimony(III)... 

Mild reduction of a yellow phosphomolybdate solution with stannous chloride yields phosphomolybdenum blue (above). This forms the basis of a sensitive method for estimating P in a variety of materials. Other reducing agents may be employed. A single reagent consisting of ammonium molybdate, hydrazine sulphate and sulphuric acid can be used. 

The chloride content was determined by the Volhard method, the H2P0 content was determined alkalimetrically after ion exchange calcium content was determined by a compleximetric titration. Where the amount of phosphate ion was small, it was determined gravimetrlcally as ammonium phosphomolybdate. 

Stannous chloride reduces not only molybdates to the colored lower oxides,2 but also reacts with phosphomolybdic acid and its salts. Molyb-denum blue results. It is an important fact, especially for the detection of tin in the presence of antimony salts, that stannous chloride will reduce not only the soluble phosphomolybdic acid as does antimony trichloride (compare page 105), but also the insoluble phosphomolybdates (e.g., the potassium or ammonium salt). Concerning molybdeniun blue see copper test 5, page 210. 

Soluble proteins may usually be precipitated by a variety of reagents, and many of them may be coagulated by heating. Some of the common salts, like ammonium sulfate, sodium sulfate, sodium chloride, etc., serve for salting out of many of these members in the unaltered condition, while certain acids (picric, tannic, phosphotungstic, phosphomolybdic, etc.) serve for their removal as insoluble salts. 

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