US Patent 11953479 Selective optical aqueous and non-aqueous detection of free sulfites

4-pyrrolylpyridine, a novel anion sensor, displays a substantial color loss upon addition of sodium sulfite in aqueous solvents. A variety of anions were tested, including halides, phosphates, sulfates, and hydroxide, but all solutions remained unchanged aside from the sulfite, which displayed bleaching. Described here is a method for which the exact concentration of sulfites in a consumer product can be determined. The test is sensitive over a broad range of sulfites, from 0.84 ppm to over 10,000 ppm, and is accurate with a standard deviation of ±0.01 ppm.