Brown FK

Description and assay

Specification history

Prepared at the 30th JECFA (1986), published in FNP 37 (1986) and in FNP 52 (1992). Metals and arsenic specifications revised at the 59th JECFA (2002). No ADI was allocated at the 30th (JECFA 1986)

Chemical names

A mixture of I Sodium 4-(2,4-diaminophenylazo) benzenesulfonate II Sodium 4-(4,6-diamino-m-tolylazo) benzenesulfonate III Disodium 4,4'-(4,6-diamino-1,3-phenylenebisazo)- di(benzenesulfonate) IV Disodium 4,4'-(2,4-diamino-1,3-phenylenebisazo)- di(benzenesulfonate) V Disodium 4,4'-(2,4-diamino-5-methyl-1,3-phenylene- bisazo)di(benzene-sulfonate) VI Trisodium 4,4',4''-(2,4-diaminobenzene-1,3,5- trisazo)tri-(benzene-sulfonate)

C.A.S. number

8062-14-4

Chemical formula

I C 12 H 11 N 4 NaO 3 S II C 13 H 13 N 4 NaO 3 S III C 18 H 14 N 6 Na 2 O 6 S 2 IV C 18 H 14 N 6 Na 2 O 6 S 2 V C 19 H 16 N 6 Na 2 O 6 S 2 VI C 24 H 17 N 8 Na 3 O 9 S 3

Formula weight

I 314.30 II 328.33 III 520.46 IV 520.46 V 534.47 VI 726.59

Assay

Not less than 70% total colouring matters. Of the total colouring matters present the proportions of the components shall not exceed: I 26% II 17% III 17% IV 16% V 20% VI 16%

DESCRIPTION

Red-brown powder or granules

FUNCTIONAL USES

Colour

METHOD OF ASSAY

Determination of the amount of component colouring matters and subsidiary colouring matters. Apparatus - Glass tank capable of holding 20 cm x 20 cm glass TLC plates. - Micrometer syringe capable of delivering 0.10 ml with a tolerance of ± 0.002 ml - Spectrophotometer Reagents: All of recognized analytical grade - Chromatography solvent: A mixture of 4 parts phenol and 1 part water by volume - Diethyl ether - Kieselgel G - Extraction solvent: Mix 100 ml 10% sodium carbonate solution with 500 ml methanol and dilute to 1 L with water Procedure Prepare a 20 x 20 cm TLC plate with a 0.5 mm thick coating of Kieselgel G. Using the micrometer syringe apply a solution containing 0.4 mg Brown FK as evenly as possible in an area near the bottom of the plate. Develop the chromatogram in the phenol/water mixture allowing the solvent to ascend the full height of the plate; then remove it from the tank and allow it to dry. The diagram shows a typical Brown FK chromatogram with the bands numerically identified. Remove each band from the plate and transfer it to a small beaker. The subsidiary colouring matters are located in the area between bands I and V. Remove this area of Kieselgel G. Transfer it to a beaker and wash it with a small quantity of ether to remove the phenol. Allow the residual ether to evaporate. Add 10 ml of extraction solvent to each beaker and swirl to extract the colour. Filter through a small filter paper and measure the absorbance versus extraction solvent in 10 mm cells at the wavelength of maximum absorption. Calculate the concentration of each component colouring matter and of the subsidiary colouring matters using the absorptivity figures given in the table below. Component Wavelength(nm) Absorptivity I 453 55.1 II 464 59.6 III 355 88.2 IV 412 70.5 V 448 60.3 VI 410 59.7 Subsidiary Colouring Matters 425 74.2 Calculation of (i) Total colouring matters content (ii) Percentages of component colours (iii) Percentage of subsidiary colours Note : Component colours are expressed as percentages of the total colouring matters present, i.e. as percentages of the sum of component colours and subsidiary colours. Subsidiary colours are expressed for the purposes of the specification limit as a percentage of the sample. Let the absorptivities of the component colours be a 1 , a 2 ....a 6 . and the absorbances of the extracts of the component colours be A 1 , A 2 ...... A 6 . Let the Absorptivity of the subsidiary colours be a 7 and the absorbance of the extract of the subsidiary colours be A 7 . The weight (in mg) of component colour I in the 10 ml extract is calculated from the expression: In a similar manner calculate the weights (W 2 , W 3 .......W 7 ) of the remaining component colours and the subsidiary colours. (i) Total colouring matters content (%) = (ii) The percentage of component colour 1 = In a similar manner calculate the percentages of the other component colours. (iii) The percentage of subsidiary colours =

Identification

Solubility (Vol. 4)

Soluble in water; sparingly soluble in ethanol

Identification of colouring matters (Vol. 4)

Passes test

Purity criteria

Loss on drying at 135 o

Not more than 30% together with chloride and sulfate calculated as sodium

(Vol. 4)

salts

Water insoluble matter (Vol. 4)

Not more than 0.2%

Lead (Vol. 4)

Not more than 2 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.”

Subsidiary colouring matters

Not more than 3.5% See description under METHOD OF ASSAY

Organic compounds other than colouring matters

Not more than - 0.7% of 4-aminobenzene-1-sulfonic acid - 0.35% of - m-phenylenediamine and 4-methyl-m-phenylenediamine See description under TESTS

Unsulfonated primary aromatic amines (Vol. 4)

Not more than 0.007% calculated as aniline (other than m-phenylene diamine and 4-methyl-m-phenylene diamine)

Ether extractable matter (Vol. 4)

Not more than 0.2%

Organic compounds other

Use liquid chromatography (see Volume 4) under the following conditions:

than colouring matters

Detector: A UV HPLC detector recording absorbances at 254 nm Column: 250 x 4 mm Li Chromosorb RP8, 7 μm Solvent system A: 0.075 M sodium acetate solution adjusted to pH 6.0 using glacial acetic acid. B: A:methanol (2:3) Flow rate: 1 ml/min Gradient: 0 min: 100% (A), 0% (B) 15 min: 0% (A), 100% (B) 20 min: 0% (A), 100% (B) 25 min: 100% (A), 0% (B)