Appendix VIII D. Complexometric Titrations

Introduce 20.0 ml of the prescribed solution into a 500 ml conical flask, add 25.0 ml of 0.1 M sodium edetate and 10 ml of a mixture of equal volumes of a 155 g/l solution of ammonium acetate R and dilute acetic acid R. Boil for 2 min, then cool. Add 50 ml of ethanol R and 3 ml of a freshly prepared 0.25 g/l solution of dithizone R in ethanol R. Titrate the excess of sodium edetate with 0.1 M zinc sulphate until the colour changes from greenish-blue to reddish-violet.

1 ml of 0.1 M sodium edetate is equivalent to 2.698 mg of Al.

Introduce the prescribed solution into a 500 ml conical flask. Dilute to 250 ml with water R and then, unless otherwise prescribed, add dropwise, with shaking, concentrated ammonia R until the mixture becomes cloudy. Add 0.5 ml of nitric acid R. Heat to about 70 °C until the cloudiness disappears completely. Add about 50 mg of xylenol orange triturate R and titrate with 0.1 M sodium edetate until the colour changes from pinkish-violet to yellow.

1 ml of 0.1 M sodium edetate is equivalent to 20.90 mg of Bi.

Introduce the prescribed solution into a 500 ml conical flask, and dilute to 300 ml with water R. Add 6.0 ml of strong sodium hydroxide solution R and about 15 mg of calconecarboxylic acid triturate R. Titrate with 0.1 M sodium edetate until the colour changes from violet to full blue.

1 ml of 0.1 M sodium edetate is equivalent to 4.008 mg of Ca.

Introduce the prescribed solution into a 500 ml conical flask and dilute to 300 ml with water R. Add 10 ml of ammonium chloride buffer solution pH 10.0 R and about 50 mg of mordant black 11 triturate R. Heat to about 40 °C then titrate at this temperature with 0.1 M sodium edetate until the colour changes from violet to full blue.

1 ml of 0.1 M sodium edetate is equivalent to 2.431 mg of Mg.

Introduce the prescribed solution into a 500 ml conical flask and dilute to 200 ml with water R. Add about 50 mg of xylenol orange triturate R and hexamethylenetetramine R until the solution becomes violet-pink. Titrate with 0.1 M sodium edetate until the violet-pink colour changes to yellow.

1 ml of 0.1 M sodium edetate is equivalent to 20.72 mg of Pb.

Introduce the prescribed solution into a 500 ml conical flask and dilute to 200 ml with water R. Add about 50 mg of xylenol orange triturate R and hexamethylenetetramine R until the solution becomes violet-pink. Add 2 g of hexamethylenetetramine R in excess. Titrate with 0.1 M sodium edetate until the violet-pink colour changes to yellow.

1 ml of 0.1 M sodium edetate is equivalent to 6.54 mg of Zn.