SOP: Determination of Dye Content in Erythrosine

GIFSQ — Global Institute for Food Safety & Quality

Principle

Erythrosine is precipitated from aqueous solution with dilute nitric acid, collected on a tared sintered funnel, washed free of nitrate, dried to constant weight, and weighed. The residue weight, corrected by the tabulated factor, gives the dye content.

Apparatus required

• 500-ml beaker
• Sintered funnel (porosity 3, diameter 5 cm) with glass rod
• Desiccator
• Drying oven (135 ± 5 °C)

Reagents

a. 1.5 N HNO₃.

b. 0.5% HNO₃ (for washing).

c. Silver nitrate solution (for testing the washings).

Procedure

Weigh 1 g of erythrosine and transfer to a 500-ml beaker

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Dissolve in 250 ml of water and add 8 ml of 1.5 N HNO₃; stir well

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Note the tare weight of the sintered funnel (porosity 3, diameter 5 cm) with the glass rod, and filter through the funnel

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Wash thoroughly with 0.5% HNO₃ until the filtrate gives no turbidity with silver nitrate

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Wash with 30 ml of water

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Dry to constant weight at 135 ± 5 °C, carefully breaking up the precipitate with the glass rod

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Cool in a desiccator and weigh

Calculation

Dye content (%) = (Wt of residue × 105.3) ÷ Wt of sample

Where,

• Wt of residue = the weight of the dried precipitate (g)
• Wt of sample = the weight of the erythrosine sample taken (g)

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.