D. MONOGRAPHS
Calcium Dihydrogen Phosphate
Primary Calcium Phosphate
Calcium Phosphate,Monobasic
Ca(H2PO4)2･nH2O (n＝1 or 0)
Mol. Wt. monohydrate
anhydrous
monocalcium dihydrogen phosphate
Content
252.07
234.05
〔anhydrous 7758-23-8〕
Calcium Dihydrogen Phosphate, when dried, contains 95.0−105.0% of
calcium dihydrogen phosphate (Ca(H2PO4)2).
Description
Calcium Dihydrogen Phosphate occurs as colorless to white
crystals or as a white powder.
Identification
(1)
Moisten Calcium Dihydrogen Phosphate with silver nitrate
solution (1 → 50). A yellow color develops.
(2)
To 0.1 g of Calcium Dihydrogen Phosphate, add 20 ml of water, and shake.
Filter, and add 5 ml of ammonium oxalate solution (1 → 30). A white precipitate is
formed.
Purity
(1)
Clarity of solution
Very slightly turbid.
Test Solution Weigh 2.0 g of Calcium Dihydrogen Phosphate, add 18 ml of water
and 2 ml of hydrochloric acid, and dissolve by heating in a water bath for 5 minutes.
(2)
Free acid and secondary salt
Weigh 1.0 g of Calcium Dihydrogen
Phosphate, add 3 ml of water, and mix while grinding. Add 100 ml of water, shake,
and add 1 drop of methyl orange TS. A red color develops. Add 1.0 ml of 1 mol/l
sodium hydroxide. The color of the solution changes to yellow.
(3)
Carbonate
Weigh 2.0 g of Calcium Dihydrogen Phosphate, add 5 ml of
water, and boil. Cool, and add 2 ml of hydrochloric acid. No effervescence occurs.
(4)
Heavy metals
Not more than 20 µgg/g as Pb.
Test Solution Weigh 1.0 g of Calcium Dihydrogen Phosphate, add 5 ml of water
and 5 ml of diluted hydrochloric acid (1 → 4), dissolve by heating, cool, add ammonia
TS until a slight precipitate is formed, dissolve the precipitate upon adding dropwise
a small amount of diluted hydrochloric acid (1 → 4), filter, if necessary, through a
filter paper for quantitative analysis (5C), and add 10 ml of hydrochloric acid−
ammonium acetate buffer (pH 3.5) and water to make 50 ml.
Control Solution To 2.0 ml of Lead Standard Solution, add 10 ml of hydrochloric
acid-ammonium acetate buffer (pH 3.5) and water to make 50 ml.
(5)
Arsenic
Not more than 4.0 µg/g as As2O3.
Test Solution Weigh 0.50 g of Calcium Dihydrogen Phosphate, and dissolve in 5
D. MONOGRAPHS
ml of diluted hydrochloric acid (1 → 4).
Apparatus Apparatus B.
Loss on Drying
Assay
Not more than 17.0% (180℃, 3 hours).
Weigh accurately about 0.8 g of Calcium Dihydrogen Phosphate,
previously dried, dissolve in 6 ml of diluted hydrochloric acid (1 → 4), and add water
to make exactly 200 ml. Proceed as directed in Method 2 under Calcium Salt
Determination, using this solution as the test solution.
1 ml of 0.02 mol/l EDTA = 4.681 mg of CaH2P2O7