Calcium and Calcium Salts

 A. To 0.2 ml of a neutral solution containing a quantity of the substance to be examined equivalent to about 0.2 mg of calcium (Ca²⁺) per millilitre or to 0.2 ml of the prescribed solution add 0.5 ml of a 2 g/l solution of glyoxal-hydroxyanil R in ethanol (96 per cent) R, 0.2 ml of dilute sodium hydroxide solution R and 0.2 ml of sodium carbonate solution R. Shake with 1 ml to 2 ml of chloroform R and add 1 ml to 2 ml of water R. The chloroform layer is coloured red.

 B. Dissolve about 20 mg of the substance to be examined or the prescribed quantity in 5 ml of acetic acid R. Add 0.5 ml of potassium ferrocyanide solution R. The solution remains clear. Add about 50 mg of ammonium chloride R. A white, crystalline precipitate is formed.

Carbonates and Bicarbonates

Introduce into a test-tube 0.1 g of the substance to be examined and suspend in 2 ml of water R or use 2 ml of the prescribed solution. Add 3 ml of dilute acetic acid R. Close the tube immediately using a stopper fitted with a glass tube bent twice at right angles. The solution or the suspension becomes effervescent and gives off a colourless and odourless gas. Heat gently and collect the gas in 5 ml of barium hydroxide solution R. A white precipitate is formed that dissolves on addition of an excess of hydrochloric acid R1.

Chlorides

 A. Dissolve in 2 ml of water R a quantity of the substance to be examined equivalent to about 2 mg of chloride (Cl^–) 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, white 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 in 2 ml of water R and add 1.5 ml of ammonia R. The precipitate dissolves easily with the possible exception of a few large particles which dissolve slowly.

 B. Introduce into a test-tube a quantity of the substance to be examined equivalent to about 15 mg of chloride (Cl^–) or the prescribed quantity. Add 0.2 g of potassium dichromate R and 1 ml of sulphuric acid R. Place a filter-paper strip impregnated with 0.1 ml of diphenylcarbazide solution R over the opening of the test-tube. The paper turns violet-red. The impregnated paper must not come into contact with the potassium dichromate.

Citrates

Dissolve in 5 ml of water R a quantity of the substance to be examined equivalent to about 50 mg of citric acid or use 5 ml of the prescribed solution. Add 0.5 ml of sulphuric acid R and 1 ml of potassium permanganate solution R. Warm until the colour of the permanganate is discharged. Add 0.5 ml of a 100 g/l solution of sodium nitroprusside R in dilute sulphuric acid R and 4 g of sulphamic acid R. Make alkaline with concentrated ammonia R, added dropwise until all the sulphamic acid has dissolved. Addition of an excess of concentrated ammonia R produces a violet colour, turning to violet-blue.

Esters

To about 30 mg of the substance to be examined or the prescribed quantity add 0.5 ml of a 70 g/l solution of hydroxylamine hydrochloride R in methanol R and 0.5 ml of a 100 g/l solution of potassium hydroxide R in ethanol (96 per cent) R. Heat to boiling, cool, acidify with dilute hydrochloric acid R and add 0.2 ml of ferric chloride solution R1 diluted ten times. A bluish-red or red colour is produced.

Iodides

 A. Dissolve a quantity of the substance to be examined equivalent to about 4 mg of iodide (I^–) in 2 ml of water R 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 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 in 2 ml of water R and add 1.5 ml of ammonia R. The precipitate does not dissolve.

 B. To 0.2 ml of a solution of the substance to be examined containing about 5 mg of iodide (I^–) per millilitre, or to 0.2 ml of the prescribed solution, add 0.5 ml of dilute sulphuric acid R, 0.1 ml of potassium dichromate solution R, 2 ml of water R and 2 ml of chloroform R. Shake for a few seconds and allow to stand. The chloroform layer is coloured violet or violet-red.

Date: 2015-12-24; view: 1033