Facile quantification of free and total sulphur dioxide in beer using a flavylium-based fluorescent probe

Accurate and convenient determination of free and total sulphur dioxide (SO₂) in beer is pivotal to guarantee the quality of beer, but the traditional assay methods are laborious, time-consuming, and dependent on experienced technician. In this study, we designed and synthesized a flavylium-based fluorescent probe Hy-S which exhibited selective response to SO₂ under both acidic conditions (pH = 4.0) and basic conditions (pH = 9.0) with low detection limits of 0.076 mg/L and 0.041 mg/L, respectively. The real beer samples were directly assayed to obtain the free SO₂ by the probe-based method while the samples were basified and diluted before spectral measurements to determine the total SO₂. Due to the advantages of fast response, convenience, accuracy and greenness, the probe-based method possesses great potential for quantification of both free and total SO₂ in beer.