FAO DIPOTASSIUM HYDROGEN PHOSPHATE.pdf

DIPOTASSIUM HYDROGEN PHOSPHATE
Prepared at the 19th JECFA(1975), published in NMRS 55B(1976)and
in FNP 52(1992). Metals and arsenic Specifications revised at the 59th
JECFA (2002). A group MTD/ of 70 mg/kg bw, as phosphorus from all
food sources, was established at the 26th JECFA(1982)
SYNONYMS
Dibasic potassium phosphate, dipotassium monophosphate, dipotassium
phosphate, dipotassium acid phosphate, secondary potassium phosphate
INS No 340(0)
DEFINITION
Chemical names
Dipotassium hydrogenphosphate dipotassium hydrogen orthophosphate,
dipotassium hydrogen monophosphate
C.A.S. number
7758-114
Chemical formula
K2HPO4
Formula weight
174.18
Assay
Not less than 98.0% after drying
DESCRIPTION
Colourless or white granular powder, crystals or masses, deliquescent
FUNCTIONAL USES Buffering agent, sequestrant, yeast food
CHARACTERSTICS
IDENTIFICATION
Solubility (Vol
Freely soluble in water, insoluble in ethano
PH(ol. 4
8.7-9.3(1in100soln
Test for potassium(Vol 4)Passes test
Test for phosphate
Passes test
(Vo.4)
Test for orthophosphate Dissolve 0. 1 g of the sample in 10 ml water, acidify slightly with dilute
(Vol. 4
acetic acid TS, and add 1 ml of silver nitrate TS A yellow precipitate is
formed
PURITY
oss on drying(Vol 4) Not more than 5%(105, 4 h
Water insoluble substances Not more than 0.2%
Fluoride
Not more than 10 mg/kg
See description under TESTS
Arsenic(Vol 4)
Not more than 3 mg/kg
Lead(Vol 4)
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
Volume4,“ Instrumental Methods.”
TESTS
PURITY TESTS
Fluoride
Place 5 g of the sample, 25 ml of water, 50 ml of perchloric acid, 5 drops
of silver nitrate solution( 1 in 2), and a few glass beads in a 250-ml
distilling flask connected with a condenser and carrying a thermometer
and a capillary tube, both of which must extend into the liquid. Connect a
small dropping funnel, filled with water, or a steam generator, to the
capillary tube. Support the flask on an asbestos mat with a hole which
exposes about one-third of the flask to the flame. Distil into a 250-ml flask
until the temperature reaches 135 Add water from the funnel or introduce
140.Continue the distillation until 225-240 ml has been collected, he
steam through the capillary to maintain the temperature between 135 and
dilute to 250 ml with water, and mix. Place a 50-ml aliquot of this solution
in a 100-ml Nessler tube. In another similar Nessler tube place 50 ml of
water as a control. Add to each tube 0.1 ml of a filtered solution of sodium
alizarinsulfonate(1 in 1000)and 1 ml of freshly prepared hydroxylamine
solution(1 in 4000), and mix well. Add, drop wise, and with stirring, 0.05 N
sodium hydroxide to the tube containing the distillate until its colour just
matches that of the control, which is faintly pink. Then add to each tube
exactly 1 ml of 0. 1 N hydrochloric acid, and mix well. From a buret
aduated in 0.05 ml, add slowly to the tube containing the distillate
enough thorium nitrate solution(1 in 40