Edition: BP 2025 (Ph. Eur. 11.6 update)
DEFINITION
Magnesium Sulfate Mixture is an oral suspension containing 40% w/v of Magnesium Sulfate Heptahydrate and 5% w/v of Light Magnesium Carbonate in a suitable vehicle with a peppermint flavour.
The mixture complies with the requirements stated under Oral Liquids and with the following requirements.
Content of magnesium sulfate heptahydrate, MgSO4,7H2O
36.0 to 44.0% w/v.
Content of magnesium carbonate, calculated as Mg
1.14 to 1.49% w/v.
IDENTIFICATION
A. Filter 10 mL of the mixture and reserve the residue. The filtrate yields reaction A characteristic of magnesium salts, Appendix VI. Wash the residue with 10 mL of water, dissolve 25 mg in 1 mL of 1M hydrochloric acid and adjust the pH to 6 to 7 with 1M sodium hydroxide. The resulting solution yields reaction A characteristic of magnesium salts, Appendix VI.
B. The residue obtained in test A yields reaction A characteristic of carbonates, Appendix VI.
C. The filtrate obtained in test A yields reaction A characteristic of sulfates, Appendix VI.
ASSAY
For magnesium sulfate heptahydrate
Boil 0.7 g with 50 mL of a mixture of equal volumes of ethanol (96%) and water, cool, filter and wash the residue with successive small quantities of the diluted ethanol until the washings are free from sulfate. Reserve the residue for the Assay for magnesium carbonate. To the combined filtrate and washings add 10 mL of ammonia buffer pH 10.9 and titrate with 0.05M disodium edetate VS using mordant black 11 solution as indicator. Each mL of 0.05M disodium edetate VS is equivalent to 12.32 mg of MgSO4,7H2O. Determine the weight per mL of the mixture, Appendix V G, and calculate the percentage of MgSO4,7H2O, weight in volume.
For magnesium carbonate
Dissolve the residue obtained in the Assay for magnesium sulfate in 10 mL of 1M hydrochloric acid and wash the filter with successive small quantities of water until the washings are free from chloride. To the combined filtrate and washings add 10 mL of ammonia buffer pH 10.9 and titrate with 0.05M disodium edetate VS using mordant black 11 solution as indicator. Each mL of 0.05M disodium edetate VS is equivalent to 1.215 mg of Mg. Using the weight per mL, calculate the percentage of Mg, weight in volume.
