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Compositional guideline: Magnesium citrate - dibasic tetrahydrate

25 September 2012

Name of the ingredient

Magnesium citrate - dibasic tetrahydrate (AAN)

Definition of the ingredient

Magnesium citrate - dibasic tetrahydrate has the molecular formula C6H6MgO7, xH2O, where x = 4.

Molecular mass: 286 (214.5 for anhydrous substance)

Table 1. Ingredient specific requirements
Test Method reference Acceptance criteria
Description
Appearance Visual White or almost white, fine hygroscopic powder
Characteristics
Solubility BP (General notice) Soluble in water, dilute hydrochloric acid and dilute nitric acid; practically insoluble in ethanol (96%)
Appearance of solution Ph Eur method 2.2.2, Method II (see Note 1) The solution is not more intensely coloured than the reference solution BY6
pH of solution Ph Eur method 2.2.3 (see Note 2) 3.5-4.5
Loss on drying (1.000 g dried in an oven for 5 h at 180±10°C Ph Eur method 2.2.32 22.2-28.2%
Identification
Citrate Ph Eur method 2.3.1 Complies
Magnesium Ph Eur method 2.3.1 Complies
Assay
Magnesium Ph Eur method 2.5.11 10.7-12.0% (dried basis)

Notes

  1. The test solution is prepared in the following manner: Dissolve 0.75g of the substance in 5 mL dilute hydrochloric acid R using heat. Cool and dilute to 30 mL with distilled water.
  2. A 2.5% solution of the substance in carbon dioxide-free water.
Table 2. Incidental constituents
Test Method reference Acceptance criteria
Incidental metals and non-metals
Heavy metals Ph Eur method 2.4.8 No more than 10 ppm
Iron Ph Eur method 2.4.9 (see Note 3) No more than 100 ppm
Other organic or inorganic impurities or toxins
Oxalates As per Ph Eur monograph 2339 No more than 280 ppm
Sulfuric acid reaction (readily carbonisable substances) Ph Eur method 2.2.2 (Method II) (see Note 4) The solution is not more intensely coloured than the reference solution Y2
Sulfates Ph Eur method 2.4.13 (see Note 5) No more than 0.2%
Calcium Ph Eur method 2.4.3 (see Note 6) No more than 0.2%
Microbiology
While substance manufacturers are encouraged to include limits for objectionable microorganisms, it is the product into which those substances are formulated that is subject to a legally binding set of criteria. The Therapeutic Goods Order No. 77 'Microbiological Standards for Medicines' mandates that any finished product which contains the ingredient, alone or in combination with other ingredients, must comply with the microbial acceptance criteria set by Clause 9 of the Order.

Notes

  1. The solution used is prepared by diluting 4 mL of the test solution (see Note 1) to 10 mL with distilled water R.
  2. Mix 0.2 g substance with 10 mL sulphuric acid R and heat in water bath at 90±1°C for 60 min. Cool rapidly.
  3. The solution used is prepared by diluting 3 mL of the test solution (see Note 1) to 15 mL with distilled water R.
  4. The solution used is prepared by taking 2 mL of the test solution (see Note 1) and 8 mL of distilled water R, and adding 0.2 mL of dilute ammonia solution R and adjusting the pH to 3.6 (according to Ph Eur method 2.2.3). Make up to a volume of 15 mL.

Key to abbreviations

BP = British Pharmacopoeia

Ph Eur = European Pharmacopoeia