Indigo® test strips detect sulfite from 10 to 500ppm, only $26.25 per 100 strips. Sulfite is commonly used on cut potatoes to prevent unsightly surface browning. You use these strips to get a rough estimate of surface sulfite levels. Be sure to read What the 10ppm level really means since this measurement must extrapolated over the entire weight of the potato.
You can test raw, peeled potatoes for sulfite easily. Simply wet the suflite test strip pad with water (distilled or deionized ideally) & press against the potato. If free sulfite is present above 10ppm, the pad will change color.
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?