Ag+–3,3′,5,5′-tetramethylbenzidine as a probe for colorimetric detection of ascorbic acid in beverages
A novel and sensitive method for ascorbic acid (AA) determination utilizing Ag+–3,3′,5,5′-tetramethylbenzidine (TMB) as a colorimetric probe was proposed. In a weak acidic medium, Ag+ could oxidize TMB to oxidized TMB (ox-TMB) and cause a blue color solution with an absorption peak centered at 652 nm. However, the addition of AA could induce the reduction of ox-TMB, leading to shallower blueness and lower absorbance. Under the selected experimental conditions, there was a good linear relationship between the decrease of absorbance (ΔA) and AA concentration in the range of 0.5–60 μM, and the detection limit was as low as 0.23 μM. The feasibility of this method was verified in commercial beverages with recoveries of 95.8–104.1%. The method has the advantages of simplicity and practicability. More importantly, no nanomaterials need to be prepared.