• British Pharmacopoeia Volume I & II
  • Monographs: Medicinal and Pharmaceutical Substances

Anhydrous Magnesium Citrate

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General Notices

(Ph. Eur. monograph 2339)

bp2013_v2_13_medicinal_and_pharmaceutical_substances_11 magnesiumcitrateanhydrous_1_2012_70_cs.png


Mg3(C6H5O7)2    451.1    3344-18-1

Ph Eur

DEFINITION

Trimagnesium bis(2-hydroxypropane-1,2,3-tricarboxylate).

Content

15.0 per cent to 16.5 per cent of Mg (dried substance).

CHARACTERS
Appearance

White or almost white, fine, slightly hygroscopic powder.

Solubility

Soluble in water, practically insoluble in ethanol (96 per cent). It dissolves in dilute hydrochloric acid.

IDENTIFICATION

A. It gives the reaction of citrates (2.3.1).

B. It gives the reaction of magnesium (2.3.1).

C. pH (see Tests).

D. Loss on drying (see Tests).

TESTS
Solution S

Dissolve 5.0 g in carbon dioxide-free water R, heating at 60 °C, cool and dilute to 100 mL with the same solvent.

Appearance of solution

Solution S is not more opalescent than reference suspension III (2.2.1) and not more intensely coloured than reference solutions Y7 or BY6 (2.2.2, Method II).

pH (2.2.3)

6.0 to 8.5 for solution S.

Oxalates

Maximum 280 ppm.

Dissolve 0.50 g in 4 mL of water R. Add 3 mL of hydrochloric acid R and 1 g of activated zinc R. Allow to stand for 5 min. Transfer the liquid to a tube containing 0.25 mL of a 10 g/L solution of phenylhydrazine hydrochloride R. Heat to boiling. Cool rapidly, transfer to a graduated cylinder and add an equal volume of hydrochloric acid R and 0.25 mL of potassium ferricyanide solution R. Shake and allow to stand for 30 min. Any pink colour in the solution is not more intense than that in a standard prepared at the same time and in the same manner using 4 mL of a 50 mg/L solution of oxalic acid R.

Sulfates (2.4.13)

Maximum 0.2 per cent.

Dilute 1.5 mL of solution S to 15 mL with distilled water R.

Calcium (2.4.3)

Maximum 0.2 per cent.

Dilute 1.0 mL of solution S to 15 mL with distilled water R.

Iron (2.4.9)

Maximum 100 ppm.

Dilute 2.0 mL of solution S to 10 mL with distilled water R.

Heavy metals (2.4.8)

Maximum 10 ppm.

Dissolve 5.0 g in 15 mL of dilute hydrochloric acid R with heating. Adjust to pH 3.5 with ammonia R and dilute to 50 mL with distilled water R. 12 mL of this solution complies with test A. Prepare the reference solution using lead standard solution (1 ppm Pb) R.

Loss on drying (2.2.32)

Maximum 3.5 per cent, determined on 1.000 g by drying in an oven at 180 ± 10 °C for 5 h.

ASSAY

Dissolve 0.150 g in 50 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 2.431 mg of Mg.

STORAGE

In a non-metallic, airtight container.

Ph Eur