A simple and highly selective 1,2,4,5-tetrazine-based colorimetric probe for HSO₃ ^- ion recognition in food

A series of 3,6-bis-substituted-1,2,4,5-tetrazine-based colorimetric probes has been developed in good yields that exhibits highly selective and sensitive colorimetric recognition of HSO₃ ^- in aqueous solution. The color of the solution containing colorimetric probes changed markedly from orange to colorless, upon the addition of HSO₃ ^-. Quantification of the absorption titration analysis shows that the detection limit of 3,6-bis(2-aminoethylamino)-1,2,4,5-tetrazine (2a) for HSO₃ ^- was 3.8 μM. It was noted that 3,6-bis-substituted-1,2,4,5-tetrazine-based colorimetric probes have a specific response toward HSO₃ ^- without interference from other 17 different anions and 16 common cations. A plausible mechanism was proposed by high-resolution mass spectroscopy analysis and NMR spectrometry analysis, involving the nucleophilic reaction of a bisulfite anion with the tetrazine ring and free radical rearrangement of ·SO₃H. Moreover, probes 2a-2c possessed applicability for sensing bisulfite in actual food samples. Therefore, the present work established a novel strategy for investigating bisulfite in food or other products.