MAGNESIUM HYDROGEN PHOSPHATE
Prepared at the 26th JECFA (1982), published in FNP 25 (1982) and in
FNP 52 (1992). Metals and arsenic specifications revised at the 63rd
JECFA (2004). A group MTDI of 70 mg/kg bw, as phosphorus from all food
sources, was established at the 26th JECFA (1982)
SYNONYMS
Magnesium phosphate, dibasic; secondary magnesium phosphate;
dimagnesium phosphate; INS No. 343(ii).
DEFINITION
Chemical names
Magnesium hydrogen orthophosphate trihydrate, magnesium salt of
phosphoric acid (1:1)
C.A.S. number
7757-86-0
Chemical formula
MgHPO4 · 3H2O
Formula weight
174.33
Assay
Not less than 96.0% on the ignited basis
DESCRIPTION
Odourless white crystalline powder
FUNCTIONAL USES Nutrient adjunct, dietary supplement, nutrient agent
CHARACTERISTICS
IDENTIFICATION
Solubility (Vol. 4)
Slightly soluble in water, soluble in dilute acids, but insoluble in ethanol
Test for phosphate
(Vol. 4)
Passes test
Test for magnesium
(Vol. 4)
Dissolve 100 mg in 0.5 ml of diluted acetic acid TS and 20 ml of water. Add
1 ml of ferric chloride TS, let stand for 5 min and filter. The filtrate gives a
positive test for Magnesium.
PURITY
Loss on ignition
Not less than 29% and not more than 36% (800±25o to constant weight)
Fluoride (Vol. 4)
Not more than 10 mg/kg (Method III)
Use 10 ml of N hydrochloric acid to dissolve the sample
Arsenic (Vol. 4)
Lead (Vol. 4)
Not more than 3 mg/kg
Not more than 4 mg/kg
Determine using an atomic absorption technique appropriate to the
specified level. The selection of sample size and method of sample
preparation may be based on the principles of the method described in
Volume 4, “Instrumental Methods.”
METHOD OF
ASSAY
Weigh accurately about 500 mg of the residue obtained in the test for Loss
on Ignition, and dissolve it by heating in a mixture of 50 ml of water and 2 ml
of hydrochloric acid. Cool, dilute to 100.0 ml with water, and mix. Transfer
50.0 ml of this solution into a 400-ml beaker, add 100 ml of water, and heat
to 55o to 60o. From a buret add 15 ml of 0.1 M disodium EDTA, add a
magnetic stirring bar, and adjust with sodium hydroxide TS to pH 10 while
stirring. Add 10 ml of ammonia-ammonium chloride buffer TS and 12 drops
of eriochrome black TS, and continue the titration with 0.1 M disodium
EDTA until the wine-red colour changes to pure blue. Calculate the weight,
in mg, of Mg2P2O7 in the residue taken by the formula:
where
V = the volume, in ml of 0.1 M disodium EDTA required in the titration of the
50.0-ml aliquot.