A: Dissolve an amount of Oral Suspension, equivalent to about 800 mg of magaldrate, in 20 mL of 3 N hydrochloric acid, dilute with water to about 50 mL, add 3 drops of methyl red TS, and proceed as directed in Identification test A under Magaldrate, beginning with “and heat to boiling.”

B: It responds to Identification test B under Magaldrate.

C: Transfer an amount of Oral Suspension, equivalent to about 1 g of magaldrate, to a 100-mL centrifuge tube. Add about 60 mL of water, cap, and shake for 3 minutes. Centrifuge the suspension, and discard the supernatant. Repeat the washing of the residue with three 60-mL portions of water. Transfer the residue to a 250-mL beaker, and heat on a steam bath to dryness: the X-ray diffraction pattern (see X-ray Diffraction 941), in the d-spacings region below 2.57 angstrom units, of the residue so obtained conforms to that of USP Magaldrate RS.

0.8(0.0282M)

Test preparation— Transfer an accurately measured quantity of Oral Suspension, equivalent to about 1 g of magaldrate, to a 100-mL volumetric flask, add 30 mL of dilute hydrochloric acid (1 in 10), shake to dissolve, dilute with water to volume, and mix.

Procedure— Transfer 10.0 mL of Test preparation to a 400-mL beaker, and proceed as directed in the test for Magnesium hydroxide content under Magaldrate, beginning with “and dilute with water to about 200 mL.” Not less than 492 mg and not more than 666 mg of magnesium hydroxide [Mg(OH)2] per g of the labeled amount of magaldrate is found.

Edetate disodium titrant— Prepare and standardize as directed in the Assay under Ammonium Alum.

Test preparation— Prepare as directed in the test for Magnesium hydroxide content.

Procedure— Transfer 10.0 mL of Test preparation and 20 mL of water to a 250-mL beaker, and proceed as directed for Procedure in the test for Aluminum hydroxide content under Magaldrate, beginning with “Add, with stirring, 25.0 mL of Edetate disodium titrant.” Not less than 321 mg and not more than 459 mg of aluminum hydroxide [Al(OH)3] per g of the labeled amount of magaldrate is found.