Sulfite is used on seafood to inhibit bacterial growth & to maintain the pinkish color in shrimp that have been shelled. Indigo® test strips detect sulfite from 10 to 500ppm. These strips also detect & accurately report bisulfite and metabisulfite.
Measure sulfite on the surface of seafood such as shrimp & by first wetting the test strip pad with water (distilled or deionized ideally) & then pressing against the food item. If free sulfite is present above 10ppm, the pad will change color. Read more in our blog on what the 10ppm level really means.
The presence of sulfites may be listed on food labels as: sulfur dioxide, potassium bisulfite, potassium metabisulfite, sodium bisulfite, sodium metabisulfite, or sodium sulfite.
For those interested in the chemistry of how these strips work, please refer to this pdf which explains the theory of how free sulfite is detected.
This Indigo® test strip indicates the presence of sulfite ion in increments of 10, 50, 100, 250, and 500ppm after 15 seconds.
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Test strips worked as described, including the red wine citric acid method. I first did some comparisons using sulfites in water. Dipping the strips and the citric acid method gave the same result, albeit a little lower than expected. Solution was mixed to 100 ppm and both strips showed about 75. Used a similar technique on red wine, although dipping does not work. Wine with no sulfites showed zero. Added and got similar readings to the water results. Thanks for the great product and the citric acid trick.
Great place for a hard to find product. Excellent price! Quick shipping.
Thanks for letting us know. This might interest you since you are in quality control: Can 10ppm of Sulfite & Quat Really Mean Zero?