SOP: Test for Presence of Formalin in Milk (Chromotropic Acid Test)

GIFSQ — Global Institute for Food Safety & Quality

1. Reagents

Chromotropic acid reagent: prepare a saturated solution of 1,8-dihydroxynaphthalene-3,6-disulfonic acid by stirring 0.5 g of the acid in 100 mL of 72% H₂SO₄. The solution is pale yellow in color.

Prepare 72% H₂SO₄ by taking 150 mL of concentrated H₂SO₄ and mixing with 100 mL of water, and cool.

2. Procedure

Dilute 100 mL milk with 100 mL water

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Acidify with a small quantity of H₃PO₄ and steam-distil the mixture

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Collect 50 mL of the distillate

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Place 5 mL of reagent in a test tube and add, with mixing, 1 mL of distillate

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Place in a boiling water bath for 15 minutes, and observe the color during the heating period

Interpretation: Presence of HCHO (formaldehyde) is indicated by the appearance of a light to deep purple color; the depth of color depends on the amount of HCHO present.

References

Official Methods of Analysis, AOAC, 21st Edition (2019); 931.08.