SOP: Sulphide Stain Test for Tinplate
GIFSQ — Global Institute for Food Safety & Quality
Principle
How tinplate resists staining by sulphur-rich foods depends partly on the food and partly on the oxide films the plate carries. Natural foods vary too much for a standard test, so chemical stand-ins are used — the one below has been shown to track the result given by peas.
Test solution
a. 1% sodium thiosulphate solution.
b. 0.1 N H₂SO₄.
c. Anionic wetting agent (Teepol).
Prepare the test solution by adding 500 ml of the H₂SO₄ solution to 1 litre of thiosulphate solution with 10 ml of Teepol — a finely divided precipitate of sulphur appears in about 2 min. Bring the solution to a boil and use immediately.
Procedure
Immerse the test sample, with no preparatory cleaning, for 2 min
↓
Examine — if the plate stays fully bright and colour-free, it resists sulphur compounds well
↓
Mix a fresh solution for every run of about six samples — the solution lasts no more than 30 min
References
- Britton, S. C. & J. H. Hancox, Sheet Metal Ind., 42, 453 (1965).
- Hoare, W. E. & S. C. Britton, Tinplate Testing, p. 40.