Barbiturates, Non-nitrogen Substituted

Dissolve about 5 mg of the substance to be examined in 3 ml of methanol R, add 0.1 ml of a solution containing 100 g/l of cobalt nitrate R and 100 g/l of calcium chloride R. Mix and add, with shaking, 0.1 ml of dilute sodium hydroxide solution R. A violet-blue colour and precipitate are formed.

Benzoates

 A. To 1 ml of the prescribed solution add 0.5 ml of ferric chloride solution R1. A dull-yellow precipitate, soluble in ether R, is formed.

 B. Place 0.2 g of the substance to be examined, treated if necessary as prescribed, in a test-tube. Moisten with 0.2 ml to 0.3 ml of sulphuric acid R. Gently warm the bottom of the tube. A white sublimate is deposited on the inner wall of the tube.

 C. Dissolve 0.5 g of the substance to be examined in 10 ml of water R or use 10 ml of the prescribed solution. Add 0.5 ml of hydrochloric acid R. The precipitate obtained, after crystallisation from warm water R and drying in vacuo, has a melting point (2.2.14) of 120 °C to 124 °C.

Bismuth and Bismuth Compounds

 A. To 0.5 g of the substance to be examined add 10 ml of dilute hydrochloric acid R or use 10 ml of the prescribed solution. Heat to boiling for 1 min. Cool and filter if necessary. To 1 ml of the solution obtained add 20 ml of water R. A white or slightly yellow precipitate is formed which on addition of 0.05 ml to 0.1 ml of sodium sulphide solution R turns brown.

 B. To about 45 mg of the substance to be examined add 10 ml of dilute nitric acid R or use 10 ml of the prescribed solution. Boil for 1 min. Allow to cool and filter if necessary. To 5 ml of the solution obtained add 2 ml of a 100 g/l solution of thiourea R. A yellowish-orange colour or an orange precipitate is formed. Add 4 ml of a 25 g/l solution of sodium fluoride R. The solution is not decolorised within 30 min.

Bromides

 A. Dissolve in 2 ml of water R a quantity of the substance to be examined equivalent to about 3 mg of bromide (Br^–) or use 2 ml of the prescribed solution. Acidify with dilute nitric acid R and add 0.4 ml of silver nitrate solution R1. Shake and allow to stand. A curdled, pale yellow precipitate is formed. Centrifuge and wash the precipitate with three quantities, each of 1 ml, of water R. Carry out this operation rapidly in subdued light disregarding the fact that the supernatant solution may not become perfectly clear. Suspend the precipitate obtained in 2 ml of water R and add 1.5 ml of ammonia R. The precipitate dissolves with difficulty.

 B. Introduce into a small test-tube a quantity of the substance to be examined equivalent to about 5 mg of bromide (Br^–) or the prescribed quantity. Add 0.25 ml of water R, about 75 mg of lead dioxide R, 0.25 ml of acetic acid R and shake gently. Dry the inside of the upper part of the test-tube with a piece of filter paper and allow to stand for 5 min. Prepare a strip of suitable filter paper of appropriate size. Impregnate it by capillarity, by dipping the tip in a drop of decolorised fuchsin solution R and introduce the impregnated part immediately into the tube. Starting from the tip, a violet colour appears within 10 s that is clearly distinguishable from the red colour of fuchsin, which may be visible on a small area at the top of the impregnated part of the paper strip.

Date: 2015-12-24; view: 902