Edition: BP 2025 (Ph. Eur. 11.6 update)
(Ph. Eur. monograph 0039)
Mg(OH)2 58.32 1309-42-8
Action and use
Antacid; osmotic laxative.
Preparations
Co-magaldrox Oral Suspension
Co-magaldrox Tablets
Magnesium Hydroxide Mixture
Ph Eur
DEFINITION
Content
95.0 per cent to 100.5 per cent of Mg(OH)2
CHARACTERS
Appearance
White or almost white, fine, amorphous powder.
Solubility
Practically insoluble in water. It dissolves in dilute acids.
IDENTIFICATION
A. Dissolve about 15 mg in 2 mL of dilute nitric acid R and neutralise with dilute sodium hydroxide solution R. The solution gives the reaction of magnesium (2.3.1).
B. Loss on ignition (see Tests).
TESTS
Solution S
Dissolve 5.0 g in a mixture of 50 mL of acetic acid R and 50 mL of distilled water R. Not more than slight effervescence is produced. Boil for 2 min, cool and dilute to 100 mL with dilute acetic acid R. Filter, if necessary, through a previously ignited and tared porcelain or silica filter crucible of suitable porosity to give a clear filtrate. Keep the residue for the test for substances insoluble in acetic acid.
Appearance of solution
Solution S is not more intensely coloured than reference solution B3 (2.2.2, Method II).
Soluble substances
Maximum 2.0 per cent.
Mix 2.00 g with 100 mL of water R and boil for 5 min. Filter whilst hot through a sintered-glass filter (40) (2.1.2), allow to cool and dilute to 100 mL with water R. Evaporate 50 mL of the filtrate to dryness and dry at 100-105 °C. The residue weighs a maximum of 20 mg.
Substances insoluble in acetic acid
Maximum 0.1 per cent.
Any residue obtained during the preparation of solution S, washed, dried, and ignited at 600 ± 50 °C, weighs not more than 5 mg.
Chlorides (2.4.4)
Maximum 0.1 per cent.
Dilute 1 mL of solution S to 15 mL with water R.
Sulfates (2.4.13)
Maximum 1.0 per cent.
Dilute 0.3 mL of solution S to 15 mL with distilled water R.
Calcium (2.4.3)
Maximum 1.5 per cent.
Dilute 1.3 mL of solution S to 150 mL with distilled water R.
Iron (2.4.9)
Maximum 0.07 per cent.
Dissolve 0.15 g in 5 mL of dilute hydrochloric acid R and dilute to 10 mL with water R. Dilute 1 mL of the solution to 10 mL with water R.
Loss on ignition
29.0 per cent to 32.5 per cent.
Heat 0.5 g gradually to 900 ± 50 °C and ignite to constant mass.
ASSAY
Dissolve 0.100 g in a mixture of 2 mL of dilute hydrochloric acid R and 20 mL of water R. Carry out the complexometric titration of magnesium (2.5.11). 1 mL of 0.1 M sodium edetate is equivalent to 5.832 mg of Mg(OH)2
Ph Eur
