Silver nitrate tests

This qualitative test is also referred to as Harrison s test since he was the first to describe it in 1912. The test specimen is either boiled or padded with a reagent containing a mixture of silver nitrate (1%), sodium thiosulphate (4%) and sodium hydroxide (4%) and then steamed. Those parts where degradation takes place due to oxycellulose or hydrocellulose in a fabric will be stained black or dark grey due to the formation of silver by reduction. 

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Procedure. Prepare an anion exchange column (Section 7.8) using about 40g of Duolite A113 (chloride form). The ion exchange tube may be 16 cm long and about 12 mm internal diameter. Wash the column with 0.6M sodium nitrate until the effluent contains no chloride ion (silver nitrate test) and then wash with 50 mL of 0.3 M sodium nitrate. 

Intermittent silver nitrate tests will indicate whether the solution is free of salts. 

BP and EP recommend that for the bromide test, a sample solution has to be first acidified with dilute nitric acid, and silver nitrate solution is added to produce a curdled, pale yellow precipitate. This precipitate will dissolve with difficulty when suspended in a solution consisting of 2 ml of water and 1.5 ml of ammonia. Unlike BP and EP, USP employs a silver nitrate test for identification of bromide. In this test, addition of silver nitrate test solution to the solution of rocuronium bromide (1 part of rocuronium bromide in 100 parts of water) will produce a white precipitate which is insoluble in nitric acid and slightly soluble in 6N ammonium hydroxide. 

Silver nitrate test The compound to be tested is treated with a few drops of 1% alcoholic silver nitrate. A white precipitate indicates a positive reaction. This could be due to either silver chloride (reaction with a reactive alkyl halide), silver alkynide (reaction with a terminal alkyne), or the silver salt of a carboxylic acid (reaction with a carboxylic acid). 

If the product contains chlorine as indicated by the alcoholic silver nitrate test, it may be purified by adding a small amount of anhydrous calcium oxide (0.5 g. per 50 g. of product) and redistilling under reduced pressure. 

Tannic acid-silver nitrate test The basis of this test is the reducing action of tannic acid (a glucoside of digallic acid) upon the silver ammine complex [Ag(NH3)2]+ to yield black silver it therefore precipitates silver in the presence of ammonia but not from a slightly acid silver nitrate solution. 

Reduction of nitrates in alkaline medium Ammonia is evolved (detected by its odour by its action upon red litmus paper and upon mercury(I) nitrate paper or by the tannic acid-silver nitrate test, Section III.38, reaction 7) when a solution of a nitrate is boiled with zinc dust or gently warmed-with aluminium powder and sodium hydroxide solution. Excellent results are obtained by the use of Devarda s alloy (45 per cent Al, 5 per cent Zn, and 50 per cent Cu). Ammonium ions must, of course, be removed by boiling the solution with sodium hydroxide solution (and, preferably, evaporating almost to dryness) before the addition of the metal. 

Attention is directed to the fact that arsenites are reduced in alkaline solution by aluminium, Devarda s alloy, etc., to arsine, which blackens mercury(I) nitrate paper and also gives a positive tannic acid-silver nitrate test. Hence neither the mercury(I) nitrate test nor the tannic acid-silver nitrate test for ammonia is applicable if arsenites are present. 

It must be emphasized that the mercury(I) nitrate paper test for ammonia is not applicable in the presence of arsenite. Arsenite is reduced by alkaline reducing agents to arsine, which blackens mercury(l) nitrate paper. The tannic acid-silver nitrate test (Section 111.38, reaction 7) may also be used this test is likewise not applicable in the presence of arsenite. 

Ammonium was tested for in preliminary test 6 (Section V.2). By heating the original substance with NaOH solution, NH3 will be evolved from ammonium salts. The NH3 gas may be identified by its odour, by its action upon red litmus paper or upon filter paper moistened with mercury(I) nitrate solution, or by the tannic a cid-silver nitrate test (Section III.38, reaction 7). The insertion of a loose plug of cotton wool in the upper part of the tube will eliminate the danger of NaOH solution spray affecting the reagent paper. 

It will be appreciated that iodate is incompatible with both iodide (cf. Section IV.21, reaction 6) and with thiocyanate (Section IV.21, reaction 9) since iodine is liberated in acid solution. Also sulphide is incompatible with both bromate and iodate (oxidation to sulphate occurs), and an arsenite is oxidized by iodate in acid solution. These facts should therefore be borne in mind when interpreting Table V.30. An independent test for iodate (test 11) is provided below this can be performed before the silver nitrate tests. 

Ammonia buffer (pH9.5), 1169 Ammonia solution, dilute, 1169 Ammonia solution, strong, 1169 Ammoniacal Silver Nitrate (test), 129 Ammonium mandelate, 718 Ammonium polysulphide solution, 1169 Ammonium sulphide solution, 1169 Amobarbital, 353 Amobarbital sodium, 353 Amodiachin, 347 Amodiaquine, 347 Amodiaquine hydrochloride, 347 Amolanone, xvii Amopyroquine, xvii Amorphan Depot, 437 Amosyt, 549... 

Aldehydes and similar reducing substances are tested for by the permanganate test. A solution of 1 g. potassium permanganate in a litre of water is made up and 1 c.c. of this is added to 100 c.c. of acetone. The colour should persist for at least thirty minutes at 15 5 in the dark. In Germany, a silver nitrate test is included to detect aldehydes these can also be detected by SchifTs reagent (fuchsine-bisulphite). Light oils also reduce ammoniacal silver nitrate. They may be tested for as follows. 

The counterion for imiprimine hydrochloride, chloride, is identified as part of the active ingredient. To carry out the test, the sample powder is dissolved in alcohol, and 2 N nitric acid is added along with 3 drops of a silver nitrate test solution. A white precipitate of silver chloride is formed, which dissolves upon addition of ammonium hydroxide, confirming the presence of the chloride ion. As chloride identification is used for the testing of the drug substance, it is not required for the formulated product. 

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