Iron oxide, black

Description and assay

Specification history

Prepared at the 69 th JECFA (2008), published in FAO JECFA Monographs 5 (2008), superseding the specifications prepared at the 63 rd JECFA (2004), published in the Combined Compendium of Food Additive Specifications, FAO JECFA Monographs 1 (2005). An ADI of 0-0.5 mg/kg bw was established at the 53 rd JECFA (1999).

Chemical names

Iron Oxide Yellow: Hydrated ferric oxide, hydrated iron (III) oxide Iron Oxide Red: Iron sesquioxide, anhydrous ferric oxide, anhydrous iron (III) oxide Iron Oxide Black: Ferroso ferric oxide, iron (II,III) oxide

C.A.S. number

Iron Oxide Yellow: 51274-00-1 Iron Oxide Red: 1309-37-1 Iron Oxide Black: 1317-61-9

Chemical formula

Iron Oxide Yellow: FeO(OH) · xH2O Iron Oxide Red: Fe2O3 Iron Oxide Black: FeO · Fe2O3

Formula weight

88.85 FeO(OH) 159.70 Fe2O3 231.55 FeO · Fe2O3

Assay

Not less than 60% of iron

DESCRIPTION

Yellow, red, brown or black powder

FUNCTIONAL USES

Colour

METHOD OF ASSAY

Weigh accurately about 0.2 g of the sample, add 10 ml of 5 N hydrochloric acid, and heat cautiously to boiling in a 200-ml conical flask until the sample has dissolved. Allow to cool, add 6 to 7 drops of 30% hydrogen peroxide solution and again heat cautiously to boiling until all the excess hydrogen peroxide has decomposed (about 2-3 min). Allow to cool, add 30 ml of water and about 2 g of potassium iodide and allow to stand for 5 min. Add 30 ml of water and titrate with 0.1 N sodium thiosulfate adding starch TS as the indicator towards the end of the titration. Each ml of 0.1N sodium thiosulfate is equivalent to 5.585 mg of Fe (III).

Identification

Solubility (Vol. 4)

Insoluble in water and organic solvents; soluble in concentrated mineral acids

Purity criteria

Loss on drying (Vol. 4)

Iron Oxide Red : Not more than 1.0% (105 ° , 4 h)

Water-soluble matter

Not more than 1.0% See description under TESTS

Arsenic (Vol. 4)

Not more than 3 mg/kg Determine by the atomic absorption hydride technique. The selection of sample size and method of sample preparation may be based on the principles of the methods described in Volume 4 (under "General Methods, Metallic Impurities").

Cadmium (Vol. 4)

Not more than 1 mg/kg Determine using an atomic absorption/ICP technique appropriate to the specified level. The selection of sample size and method of sample preparation may be based on the principles of the methods described in Volume 4 (under “General Methods, Metallic Impurities”).

Lead (Vol. 4)

Not more than 10 mg/kg Determine using an atomic absorption/ICP technique appropriate to the specified level. The selection of sample size and method of sample preparation may be based on the principles of the methods described in Volume 4 (under “General Methods, Metallic Impurities”).

Mercury (Vol. 4)

Not more than 1 mg/kg Determine by the cold vapour atomic absorption technique.

Test: Water-soluble matter

Weigh accurately 5.0 g of iron oxide, transfer to a 250 ml beaker, add 200 ml of water and boil for 5 minutes; stir to avoid bumping. Cool the mixture, transfer the contents to a 250 ml volumetric flask, rinse the beaker with 25 ml of water, adding the rinsings to the flask; bring to volume with water and mix. Allow the mixture to stand for 10 minutes and filter the solution. Transfer 100 ml of filtrate into a clean dry tared beaker and carefully evaporate the solution to dryness on a boiling water bath. Dry the residue at 105 -110 o for 2 hours, cool the beaker with residue in a desiccator, weigh the beaker, and calculate the amount of residue. Water-soluble matter (%) = 250 x WR/WS where WR is the weight of residue (g) and WS is the weight of sample taken (g).